Activity Booklet - eduBuzz.org · 2014. 10. 7. · These coils are called field or stationary coils and are fixed in the casing to form the stator. If the coils are stationary, then

PHYSICS

National 4 and 5

Activity Booklet Unit 3

Electricity and Energy

North Berwick High School

Department of Physics

PHYSICS National 4/5 Electricity and Energy

2

National 4 National 4/5 National 5

Activity 1 Activity 2 Activity 3 Activity 4 Activity 5 Activity 6 Activity 7 Activity 8 Activity 9 Activity 10 Activity 11 Activity 12 Activity 13 Activity 14 Activity 15 Activity 16 Activity 17 Activity 18 Activity 19 Activity 20 Activity 21 Activity 22 Activity 23 Activity 24 Activity 25 Activity 26 Activity 27 Activity 28

Activity 29 Activity 30 Activity 31 Activity 32 Activity 33 Activity 34 Activity 35 Activity 36 Activity 37 Activity 38 Activity 39

Activity 40 Activity 41 Activity 42 Activity 43 - 49


1

ACTIVITY 1 National 4

Title: Induced Voltage (or Current)

Aim: To investigate factors affecting an induced voltage (or current) in a conductor.

Apparatus: 2 bar magnets, analogue micro-ammeter, 2 connecting leads, 2400 turn transformer coil.

Instructions:

Copy the table.

Maximum Induced Current Factor Description Smaller Same Larger

Speed of movement

Slow

Fast

Number of coils

Lower

Higher

Strength of magnetic field

Smaller

Larger Please the appropriate box in above table.

Connect the transformer coil (1200 turns) to the meter. Move one of the magnets in and out of the centre of the coil while

watching the meter. Adjust the speed of movement of the magnet and complete the

table with your observations. Alter the number of coils to 2400. Move one of the magnets in and out of the centre of the coil while

watching the meter and complete the table with your observations. Join two magnets together and move the two magnets in and out of

the centre of the coil while watching the meter and complete the table with your observations.

Write a conclusion based on the results of your investigation, include whether the voltage (or current) produced is a.c. or d.c.


2


Title: Generators

Aim: To learn about the process of generating electricity.

Apparatus: Bicycle dynamo, oscilloscope, car alternator, data projector, internet access.

Websites for possible use:

http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/electric_circuits/mainsproducedrev2.shtml

http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/electric_circuits/mainsproducedrev3.shtml

http://www.vjc.moe.edu.sg/fasttrack/physics/Generator.dcr

http://educypedia.karadimov.info/library/ace11705.swf

http://www.walter-fendt.de/ph14e/generator_e.htm

Bicycle Dynamo

Dynamo apparatus Bicycle dynamo

Instructions:

Connect the dynamo apparatus to the oscilloscope and turn the handle.

Observe the trace on the oscilloscope screen when the handle is turned at different speeds.

http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/electric_circuits/mainsproducedrev2.shtmlhttp://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/electric_circuits/mainsproducedrev2.shtmlhttp://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/electric_circuits/mainsproducedrev3.shtmlhttp://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/electric_circuits/mainsproducedrev3.shtmlhttp://www.vjc.moe.edu.sg/fasttrack/physics/Generator.dcrhttp://www.vjc.moe.edu.sg/fasttrack/physics/Generator.dcrhttp://educypedia.karadimov.info/library/ace11705.swfhttp://educypedia.karadimov.info/library/ace11705.swfhttp://www.walter-fendt.de/ph14e/generator_e.htmhttp://www.walter-fendt.de/ph14e/generator_e.htm


3

Alternators An alternator is the commonest type of a.c. generator – there is one in every modern car to keep the battery charged up. A typical alternator might produce up to 50A of electric current. Brushes cannot handle this size of current, and so an alternator, like the bicycle dynamo, has coils that do not rotate.

These coils are called field or stationary coils and are fixed in the casing to form the stator. If the coils are stationary, then the magnetic field must move. The magnetic field is created by a rotating electromagnet. The windings of these coils are in alternate directions so that the north and south poles are produced

alternately. This assembly is called the rotor. The small amount of current needed to make the rotor coil into an electromagnet comes to it from the battery through special brushes called slip rings. The alternator rotates very fast, perhaps 200 times a second, and produces a substantial amount of heat. A fan is usually connected to the alternator shaft to keep it cool. The diagram below shows the alternator from a portable generator.


4


Title: Sources of Energy

Aim: To investigate renewable and non-renewable sources of energy.

Apparatus: Poster paper, poster pens, Exploring Science textbook, Virtual Physics, website http://home.clara.net/darvill/altenerg/index.htm

The website you are asked to visit discusses ten different sources of energy. Some of them, like fossil fuels, are finite meaning that they will run out. Once we have used them up it will be impossible to replace them and so they are considered non-renewable. We will increasingly need to use renewable sources like wind.

Instructions:

For the source(s) of energy assigned to you by your teacher design an informative poster.

The poster should describe the source of energy, state whether it is re-newable or non-renewable, and explain the advantages or disadvantages associated with this source of energy.

Present your poster to the rest of the group.

http://home.clara.net/darvill/altenerg/index.htm


5


Title: Power Stations

Aim: To research the different methods of electricity production.

Apparatus: Virtual National 4 Physics, Exploring Science Book 9

Instructions:

Read Exploring Science Book 9: Pgs. 106-107

1. Copy the diagram at the top of the page. Label the separate sections.

2. Open Virtual National 4 Physics and look up 'Electricity and Energy' and open 'Generation of Energy'.

There are 5 methods to generate electricity contained on this page.

a) Write down a heading for each method and describe briefly, how each method works. Diagrams will help.

b) What part must all generators contain?

c) Open the 'Distribution of Energy' section. Copy the diagram showing how electricity gets to our home and industry.

d) Explain why transformers need to be used in the National Grid.

3. Research.

Find out what a transformer is. Draw a block diagram with the parts labelled. What are the two main types of transformer? Why do we need transformers? Where can you find transformers (apart from the National Grid)? (Your teacher may demonstrate a model of the National Grid.)


6


Title: The National Grid

Aim: To describe the transmission of energy by the National Grid and consider the advantages and disadvantages of underground/overhead distribution.

Apparatus: Summary notes, data projector, internet access.

‘How is electricity brought to our homes?’

http://www.bbc.co.uk/learningzone/clips/where-does-electricity-come-from/2413.html

‘Working to maintain the National Grid’

http://www.bbc.co.uk/learningzone/clips/working-to-maintain-the-national-grid/7407.html

Instructions:

Watch the video clips ‘Where Does Electricity Come From’ and ‘Working to Maintain the National Grid’.

Read your summary notes on ‘The National Grid’ and ‘Overhead or underground power cables’.

Copy and complete the following passage.

The __________ Grid is a system of transmission lines carrying __________ from the power stations to our homes and __________. The __________ lines are held aloft by electricity pylons or buried underground. The transmission lines __________ up when a current flows through them. In order to reduce the amount of heating the current is reduced. This can be done by using a step up __________. While these transformers step up the __________ they also step down the current. Power stations produce electricity at a voltage of __________ which is transformed to a maximum of 400 000V for transportation around the grid. Step down transformers reduce the voltage to the mains voltage of 230V. While __________ power lines are less expensive to install and maintain they are __________, spoiling the landscape. They can be more __________ to damage from severe bad weather but can last __________ as long as underground cables.

http://www.bbc.co.uk/learningzone/clips/where-does-electricity-come-from/2413.htmlhttp://www.bbc.co.uk/learningzone/clips/where-does-electricity-come-from/2413.htmlhttp://www.bbc.co.uk/learningzone/clips/working-to-maintain-the-national-grid/7407.htmlhttp://www.bbc.co.uk/learningzone/clips/working-to-maintain-the-national-grid/7407.html


7


Title: Electrostatics

Aim: To investigate the interaction of charged objects.

Apparatus: Van de Graaff generator, polythene rods, acetate rods, duster, 2 watch glasses.

Rubbing a polythene rod with a duster will charge it negatively. Rubbing an acetate rod with a duster charges it positively.

Instructions:

Pupil Experiment

Copy and complete the table below.

Effect

Charged Rod Attracts Repels

Polythene (-ve) Polythene (-ve) Acetate (+ve) Acetate (+ve)

Polythene (-ve) Acetate (+ve)

In your conclusion state what you observed for like and unlike

charges.

Teacher Demonstration Watch the teacher demonstration of the Van de Graaff.

Watch glasses

Charged rod


8

Some Applications of Electrostatics

Photocopiers

Electrostatic dust precipitators

Smoke is produced when fossil fuels burn. Smoke is made of tiny solid particles, such as carbon. To remove these particles from the waste gases an electrostatic precipitator is used.


9

Car Paint Spraying

Car manufacturers can save money by using charged paint spray guns. They work because like charges repel and unlike charges attract.

The spray gun is charged positively, which causes every paint particle to become positively charged. Like charges repel and the paint particles spread out. The object to be painted is given a negative charge and so attracts the paint particles. The advantages of using this system are that less paint is wasted, the object receives an even coat and the paint covers awkward ‘shadow’ surfaces that the operator cannot see.


10


Title: Alternating and Direct Current (a.c. and d.c.)

Aim: To observe a.c. and d.c. signals on an oscilloscope.

Apparatus: 1.5V cell, Unilab 1V supply, oscilloscope, leads.

Instructions:

Switch on the oscilloscope and adjust it to give a horizontal line in the centre of the screen.

Connect the leads from the battery (d.c.) to the Y-input of the oscilloscope.

Draw the signal you see on the screen on a grid. Reverse the connections to the battery. Draw the new signal on another grid. Replace the battery with the transformer (a.c.). Adjust the controls of the oscilloscope to make a steady pattern. Draw the new signal.


11


Title: Charge, Current, and Time

Aim: To practise using the formula that links charge, current, and time.

Apparatus: None.

Electric current is defined as the amount of charge per second flowing round a circuit. This definition leads to the formula:

I = Q/t

However, this formula is more commonly known as:

Q = It

Where Q: charge measured in coulombs (C)

I: current measured in amperes (A)

t: time measured in seconds (s)

Instructions:

Complete Electrical Current problem sheet.


12


Title: Electric Fields

Aim: To observe the effect of an electric field on a negative charge.

Apparatus: Cathode ray deflection tube and stand, EHT supply (for electron gun and heater), HT supply (for deflection plates).

An electric field is a region of space in which a charge placed in that region will experience a force.

Below is a diagram of the electric field between two parallel charged plates. The normally invisible electric field lines have been drawn to show the direction of the electric field.

The diagram shows the positive charge being accelerated towards the negative plate, due to both repulsion of the positive plate and the attraction to the negative plate.

The direction of the electric field is the

direction of the force experienced by a

positive charge placed in the field.

+ + + +

+

- - - -

+


13

If a negative charge was placed in the electric field it would be accelerated towards the positive plate, due to both repulsion of the negative plate and the attraction to the positive plate.

The parallel plates will have a voltage across them this called the potential difference, symbol V, measured in volts, V.

The potential difference is a measure of the energy given to the charges when they move between the plates.

Potential difference is equal to the work done in moving one coulomb of charge between the plates. Therefore a potential difference of one volt indicates that one joule of energy is being used to move one coulomb of charge between the plates.

Instructions:

Watch the teacher demonstration of the deflection tube.


14

ACTIVITY 10 National 4 and 5

Title: Measuring Current

Aim: To learn how to measure the current through components using an ammeter.

Apparatus: Lap pack, two 2.5V lamps, connecting leads, ammeter.

Materials can be divided into two main groups, conductors and insulators. Electrical conductors contain electrons which are free to move throughout the structure. In electrical insulators, the electrons are tightly bound and cannot move. All circuits need a source of energy and some electrical components, connected by wires. The source of energy may be a battery or the mains. If a battery is connected across a conductor such as a bulb, then the electrons will move in one direction around the circuit. An electric current (symbol I) is the flow of electrons around a circuit. The greater the flow of electrons in a circuit, the greater is the current. The current through a component can be measured using an ammeter connected in series. The ampere (A) is the unit of current.

Circuit 1 Circuit 2

Instructions:

Connect up circuit 1 setting the lap pack to 4V. To measure the current through the lamps add an ammeter to

the circuit as in circuit 2 (listen carefully to your teachers instructions on how to do this).

If a negative reading is obtained swap the terminals. Record the current through the lamps.

A


15


Title: Measuring Voltage

Aim: To learn how to measure the voltage across components using a voltmeter.

Apparatus: Lap pack, two 2.5V lamps, connecting leads, voltmeter.

Voltage (symbol V) is a measure of the energy given to the charges flowing round a circuit by the battery (or mains). The voltage across a component can be measured using a voltmeter connected in parallel. The volt (V) is the unit of voltage.

Circuit 1 Circuit 2

Instructions:

Connect up circuit 1 setting the lap pack to 4V. To measure the voltage across the lamps add a voltmeter to the

circuit as in circuit 2 (listen carefully to your teachers instructions on how to do this).

If a negative reading is obtained swap the terminals. Record the voltage across the lamps.

- +


16


Title: Current and Voltage in Series and Parallel Circuits

Aim: To establish the rules for current and voltage in series and parallel circuits.

Apparatus: Series and parallel circuit boards with multimeters.

Circuit 1 – Series Circuit Circuit 2 – Parallel Circuit

Instructions:

Collect a pupil worksheet. Build the series circuit shown on the left side of the sheet. Make a table with the ammeter readings and voltmeter readings. Build the parallel circuit shown on the right side of the sheet. Make a table with the ammeter readings and voltmeter readings.


17


Title: Measuring Resistance

Aim: To learn how to measure the resistance of components using an ohmmeter.

Apparatus: Resistors A - C, connecting leads, ohmmeter.

Electrical resistance (symbol R) is the opposition to the flow of electric current. The resistance of a component (or circuit) can be measured using an ohmmeter. The ohm (Ω) is the unit of resistance.

Note that resistance should only be measured once the voltage supply has been removed from the circuit.

Instructions:

Copy the table below.

Resistor Measured resistance (Ω)

Two leads

A

B

C

To measure the resistance of the leads and resistors connect an ohmmeter across the resistors (listen carefully to your teachers instructions on how to do this).

If a 1 on the LHS of the display is obtained increase the range on the dial.

Ohmmeter

resistor

Ω


18


Title: Current and Resistance

Aim: To find the relationship between current and resistance.

Apparatus: Lap pack, 2.5V lamp, connecting leads, ammeter, resistors A - D.

Circuit 1 Circuit 2

Instructions:


Resistor Resistance (Ω) Current (A)

No resistor N/A

A

B

C

D

Enter the values of the four resistors in the table. Set up Circuit 1 with no resistors and take the reading on the

ammeter. Record the current reading on the ammeter in the table. Set up Circuit 2 with the first resistor (select resistor A first) and

take the current reading. Without changing the supply voltage, repeat the current reading

for the other resistors. Conclude the relationship for resistance and current.

+ - Low Voltage Supply

A R

+ - Low Voltage Supply

A


19


Title: Ohm’s Law

Aim: To find the relationship between current, voltage, and resistance.

Apparatus: Lap pack, connecting leads, 2 multimeters, resistors A - D.

Circuit 1 Circuit 2

Instructions:


Resistor Resistance (R) using circuit 1

(Ω)

Voltage (V) across

resistor (volts)

Current (I) through resistor

(amperes)

Voltage (V) divided by current (I)

A

B

C

D

Use Circuit 1 to measure the resistances of resistors A, B, C and D

and enter your values in your table headed Resistance. Setup Circuit 2 using Resistor A. Measure the voltage (V) across Resistor A and the current (I)

through resistor A and enter the values in Column 3 and Column 4.

Repeat voltage and current readings for Resistors B, C and D. Compare the values in the two shaded columns (Resistance and

V/I). Conclude the relationship between current, voltage, and

resistance.

resistor

Ω

A resistor

Labpack

-

+


20

+

-

Variable

Low voltage

supply

A resistor A

ACTIVITY 15 (continued) National 5 extension

Title: Ohm’s Law (continued)

Instructions:


Set up the Ohm’s Law Circuit exactly as above. Vary the voltage across resistor X so that 5 voltages and currents

can be measured. Enter your readings into the table. What do you notice about V/I for different values of current? Plot a graph of voltage against current. Find the gradient of the line. What conclusion can you make about the resistance of a resistor

when the current through it changes?

Voltage (V) across resistor A

Current (I) through resistor X

Voltage (V) / Current (I)


21


Title: Factors Affecting Resistance (Material, Length, and Thickness)

Aim: To investigate the resistance of different metals and find the relationship between resistance and length, and resistance and thickness.

Apparatus: 3 lengths of wire of same thickness and length (nichrome, copper, iron), 3 thicknesses of nichrome, 3 lengths of nichrome, ohmmeter, connecting leads.

Instructions:

Copy the tables.

Material R (Ω) Length of Nichrome

R (Ω) Thickness of

Nichrome R (Ω)

Copper Short Thinnest

Nichrome Medium Thicker Iron Long Thickest

Measure the resistance of the copper, nichrome, and nichrome.

Make sure the thicknesses and lengths are the same. Complete the first table. Measure the resistance of nichrome at three different lengths.

Make sure the thickness is the same for each wire. Complete the second table. Measure the resistance of nichrome at three different

thicknesses. Make sure the lengths are the same for each wire. Complete the third table. Write a conclusion based on your results.

Ω


22


Title: Factors Affecting Resistance (Temperature)

Aim: To investigate the relationship between resistance and temperature.

Apparatus: 6V lamp, variable power supply, 2 multimeters, connecting leads.

Instructions:

Copy the table.

Voltage across lamp (V)

Current through lamp (A)

Resistance of lamp (Ω)

Set up the circuit as in the diagram setting the supply voltage to

1V Record the current through and voltage across the lamp in your

table. Increase the supply voltage to 2V then increase 1V at a time up to

6V recording the current and voltage each time. Calculate the resistance of the lamp using Ohm’s Law (V = IR). Write a conclusion based on your results (remember as the lamp

gets brighter the temperature increases).

- +

A

V


23


Title: Electronic Systems - Introduction

Aim: To learn the three parts of an electronic system.

Apparatus: None.

Every electronic system is made up of three parts. They are the input, process and output of the system. This can be shown in a diagram called a block diagram. It looks like this:

The following shows the block diagram for a system that sounds an alarm when the temperature in a room gets too low.

output process input

buzzer processor Temperature

sensor


24


Title: Electronic Systems – Analogue or Digital

Aim: To study analogue and digital signals using an oscilloscope.

Apparatus: Phillips Harris signal generator, oscilloscope, microphone.

The output of an electronic system can be either analogue or digital.

Analogue and digital signals can be identified from their waveform as shown. A is analogue and B is digital.

Digital outputs can only have two values they can either be on or off. Analogue outputs have continuously varying values.

A B

Microphone

Oscilloscope

Pulse generator

Oscilloscope

Circuit diagrams Block diagrams

Instructions:

Draw the trace you see on the oscilloscope for each circuit. Label your traces as analogue or digital.

Pulse

generator


25


Title: Input Device – The Microphone

Aim: To investigate the function of a microphone.

Apparatus: Microphone, oscilloscope.

The microphone is an input device that changes sound energy into electrical energy.

Microphone

Oscilloscope

Circuit Diagram Block Diagram

Instructions:

Connect the microphone to the input terminals of the oscilloscope.

Adjust the controls of the oscilloscope so that there is a clear pattern on the screen when you make sounds into the microphone.

Try speaking different letters into the microphone of different volumes and pitch.

Draw some of the traces you see into your jotter below your block diagram.

Conclude whether the microphone is an analogue or digital device.


26


Title: Input Devices – The Thermistor, Light Dependent Resistor (LDR), and Switch

Aim: To investigate the resistance of a thermistor, LDR and switch.

Apparatus: Thermistor, LDR, switch, ohmmeter, connecting leads.

Thermistor

Ohmmeter

LDR

Ohmmeter

Switch

Ohmmeter

Circuit Diagrams Block Diagrams

Instructions:

Copy the table.

Input Device Condition Resistance (high or low?)

Thermistor Cold

Warm

LDR In light

In darkness

Switch On

Off

Build each of the circuits in turn and complete the table. In your conclusion comment on how the conditions affect the

resistance for each component.

Ω

Ω

Ω


27


Title: Input Devices – The Photovoltaic Cell and the Capacitor

Aim: To investigate the voltage across a photovoltaic cell and capacitor.

Apparatus: Photovoltaic cell, selection of capacitors, selection of resistors, voltmeter, coloured filters.

Photovoltaic cell

Voltmeter

Capacitor

Voltmeter


Instructions:

Photovoltaic Cell Build the photovoltaic cell circuit. Measure the voltage with the cell in light and darkness. Change the colour of the light by placing a coloured filter over

the cell. Conclude the effect altering the lighting conditions has on the

voltage.

Capacitor Build the capacitor circuit. Monitor the voltage as the capacitor is charging. Repeat this for different values of resistance and capacitance. Your conclusion should include what you notice about the

voltage across a discharged, charging, and fully charged capacitor. You should also comment on the effect increasing the resistance and/or capacitance has on the time it takes the capacitor to fully charge.

V

V


28


Title: Output Devices – The Loudspeaker and the Buzzer

Aim: To investigate output devices that change electrical energy to sound energy.

Apparatus: Signal generator, loudspeaker (with polystyrene balls), 4.5V battery, and buzzer.

A loudspeaker usually consists of a paper cone, which is attached to a fine coil of wire suspended between the poles of a permanent magnet. When a varying current passes through the coil it becomes magnetized and reacts with the permanent magnet to move the cone backwards and forwards, producing sound waves in the surrounding air.

Signal generator

Loudspeaker

Power supply

Buzzer


Instructions:

Build both circuits. In your conclusions comment on whether the devices are

analogue or digital.

G


29


Title: Output Devices – The Solenoid, Motor, and Relay Switch

Aim: To investigate output devices that change electrical energy to kinetic energy.

Apparatus: Solenoid and alpha connectors, motor, 4.5V battery, variable power supply, relay switch circuit (electromagnetic relay, motor, lab pack, switch, 4.5V battery).

Power supply

Solenoid

Variable power supply

Motor


Instructions:

Build both circuits. In your conclusions comment on whether the devices are

analogue or digital. Copy the diagram below of the relay switch circuit.

Watch your teacher demonstrate its use.

M


30


Title: Output Devices – The Filament Lamp and Light Emitting Diode (LED

Aim: To investigate output devices that change electrical energy to light energy.

Apparatus: 2.5V lamp, LED, multimeter, 4.5V battery, connecting leads.


Lamp


LED


Instructions:

Build the lamp and LED circuit. In your conclusion comment on which device is analogue and

which is digital, which uses the higher current, and which device needs to be orientated correctly to operate.

A

A


31


Title: The Angus System Board

Aim: To become familiar with the Angus System Board.

Apparatus: Angus System Board, battery pack, small connecting leads.

TESTING GATES – use push switches as inputs

and the test probe as output to

check truth tables for NOT, AND,

OR gates.

LDR – alter

characteristics by

slipping a short piece of

tubing over LDR.

Thermistor – warm with

thumb or heel of hand.

Do not rub.

Set the switching

temperature by adjusting

resistor.

Use a 5V supply or the

battery pack provided.

Connections to GATES

Use pre-wired plug-on

connector to connect

torch, fan etc to the relay.


32


Title: Logic Gates

Aim: To determine the truth tables for the NOT, AND, and OR gate.

Apparatus: Angus System Board, battery pack, small connecting leads. Instructions:

Copy the information below. Use the Angus System Board to complete the truth tables for the three gates.

NOT Gate (inverter)

Truth Table

Input Output 0

1 The output from the NOT gate is ________ what you put in.

AND Gate

Truth Table

Inputs A B Output

0 0

0 1 1 0

1 1 The output from the AND gate is high if input A ________ input B are ________ .

OR Gate

Truth Table

Inputs A B Output

0 0 0 1

1 0

1 1 The output from the OR gate is high if input A ________ input B is high.


33


Title: Combining Logic Gates

Aim: To combine logic gates for control in simple situations.

Apparatus: Angus System Board, battery pack, small connecting leads.

Input Devices

Logic States

Gates Output Devices

Logic States

Light Sensor Bright 1 Dark 0

NOT Make

sure you know the

truth tables

for these gates.

Lamp On 1 Off 0

Temperature Sensor

Hot 1 Cold 0

AND Buzzer On 1 Off 0

Switches On 1 Off 0

OR Motor On 1 Off 0

Relay

Switch On 1 Off 0

Instructions: Using the input devices, gates, and output devices above design solutions to the following problems (include the circuit diagram and truth table).

Problem 1 People in an office find it gets too hot in the summer. An electronic system is required to turn the motor of a fan on when it is too hot. Problem 2 At certain times of the year a farmer would like an alarm to wake him up when it gets light. He would like his alarm to sound only when it gets light and when he has switched it on. Problem 3 A shop has had a number of break-ins at night. The shopkeeper wants an electronic system to turn a light on at night. Problem 4 Many outdoor lights are also used as security devices. An electronic system is required that turns on a lamp when heat is detected during the hours of darkness.


34


Title: Resistance in Series

Aim: To investigate the relationship for calculating the total resistance in a series circuit.

Apparatus: Multimeter (ohmmeter), series circuit board, connecting leads.

Note: there is no power supply attached to the circuit when measuring resistance with an ohmmeter

Circuit 1 – Measuring the resistance of 1 resistor using an ohmmeter.

Circuit 2 – Measuring the resistance of all 3 resistors connected in series

using an ohmmeter.

Instructions:

Copy the table.

Resistor Resistance (Ω)

R1 R2

R3 RT

Measure the resistance of each resistor in turn using circuit 1. Record the readings in your table. Measure the resistance of all three resistors using circuit 2. Record the reading in your table. Write a conclusion stating the relationship between RT, R1, R2,

and R3.

Ω

Ω


35


Title: Resistance in Parallel

Aim: To investigate the relationship for calculating the total resistance in a parallel circuit.

Apparatus: Multimeter (ohmmeter), 2 resistors, connecting leads.

Note: there is no power supply attached to the circuit when measuring resistance with an ohmmeter

Circuit 1 – Measuring the resistance of 1 resistor using an ohmmeter.

Circuit 2 – Measuring the resistance of both resistors connected in parallel using an ohmmeter.

Instructions:

Copy the table. R1 (Ω)

R2 (Ω)

1/R1 1/R2 1/R1 + 1/R2

1/RT

Measure the resistance of each resistor in turn using circuit 1. Measure the resistance of both resistors using circuit 2. Write a conclusion stating the relationship between 1/RT,

1/R1, and 1/R2.

Ω

Ω


36


Title: Fuses

Aim: To draw and identify the circuit symbol for a fuse and give an example of its use in a practical situation.

A fuse is a sacrificial safety device which melts if the current in the circuit is too high thus ‘breaking’ the circuit and cutting of the power supply. They are used to protect flexes and household wiring from overheating, and prevent damage to electrical and electronic devices. A fuse is usually constructed using a thin metal strip or filament encased in a protective transparent glass or plastic enclosure. Fuses are available in pre-defined ratings, such as 1A, 5A, 13A, 15A, 25A, 30A etc. Plugs on electrical devices have a fuse in the live wire. The value of this fuse is determined by the power rating of the appliance. High power ratings (>700W require a 13A fuse) whereas low power ratings (≤700W) require a 3A fuse. Modern household wiring is protected by circuit breakers – a type of fuse that can be reset once it has ‘tripped’.

The fuse works with the Earth wire to protect the user if the metal casing becomes ‘live’. This can happen if the flex wiring becomes loose and touches the metal casing. Without the protection of the fuse and Earth wire the user would be electrocuted if they touched this live casing. The Earth wire is attached to the metal casing. If the metal casing becomes ‘live’ the high current drawn from the supply flows through the Earth wire (in preference the user touching the appliance) and at the same time the high current melts the fuse cutting of the power to the appliance.

Instructions:

The __________ wire is a __________ device which is connected to the __________ of appliances. The Earth wire provides a __________ for the electrical __________ to flow if the live wire becomes __________ and touches the casing making it __________ . The large __________ which flows through the Earth wire will __________ the fuse switching the _________ off.


37


Title: Voltage Divider Circuits

Aim: To establish a formula relating resistance and voltage for a voltage divider circuit.

Apparatus: 1.5V cell, six pairs of resistors, multimeter, connecting leads.

Note: The pairs of resistors in this activity are – pair 1 (1kΩ & 1kΩ), pair 2 (1.2kΩ & 1.8kΩ), pair 3 (3.3kΩ & 3.3kΩ), pair 4 (3.3kΩ & 8.2kΩ), pair 5 (10kΩ & 8.2kΩ), and pair 6 (3.3kΩ & 1.2kΩ).

Circuit Diagrams

Circuit 1

Circuit 2

Instructions:

Copy the table.

Pair R1 (Ω) R2 (Ω) R1/R2 V1 (V) V2 (V) V1/V2

1 2

3 4

5

6 For a pair of resistors measure the actual value of resistance

of each using an ohmmeter (see circuit 1) noting the values in the table.

Set up circuit 2 for the pair of resistors you have chosen. Use the voltmeter to measure the voltage across each

resistor. Calculate R1/R2 and V1/V2. If time, repeat for another pair of resistors. Conclude the formula that relates the resistances and

voltages in a voltage divider circuit.

Ω

R1

R2


38


Title: The Transistor as a Switch

Aim: To establish the required base-emitter voltage for the npn transistor to conduct and the required gate-source voltage for the MOSFET to conduct.

Apparatus: 4.5V battery, potential divider (board 70), 4.7k potentiometer, transistor switch/indicator (board 41), alpha links, n-channel enhancement MOSFET, lamp, multimeter, connecting leads.

Block Diagram

Potentiometer npn transistor

OR MOSFET

Output Device

Circuit Diagram (npn transistor)

Circuit Diagram (MOSFET transistor)

V

4.5 V

0 V

b

c

e


39

Instructions:

Set up the circuit with the npn transistor as shown. With the LED off, slowly turn the potentiometer clockwise

and stop as soon as the LED is fully on. Note the voltage across the base-emitter terminals of the

transistor when the LED is fully on. Replace the npn transistor board with the MOSFET transistor

board and use the lamp for the output device. With the lamp off, slowly turn the potentiometer clockwise

and stop as soon as the lamp is fully on. Note the voltage across the gate-source terminals of the

transistor when the LED is fully on.

Note: In Activities 34, 35, and 36 the transistor used is an npn transistor. This could be replaced with a MOSFET and the circuit would operate in the same way with the only difference being that a higher voltage across the gate-source terminals would be required to make the MOSFET conduct.


40


Title: Light Controlled Switch

Aim: To observe and describe the operation of a simple transistor switching circuit controlled by light.

Apparatus: 4.5V battery, potential divider (board 70), LDR, 4.7k variable resistor, transistor switch/indicator (board 41), alpha links, connecting leads.

Block Diagram

Voltage Divider Circuit

(containing LDR)

Transistor Switch

Output Device

Circuit Diagram

Instructions:

Set up the circuit as shown. Adjust the variable resistor until the LED is off (just). Cover the LDR and watch what happens to the LED. Describe the operation of the circuit at each stage (input,

process, and output). Suggest a use for this circuit. Redesign the circuit so that the LED turns off when it is dark. Draw the circuit diagram for this circuit. Describe the operation of this circuit at each stage (input,

process, and output). Suggest a use for this circuit.

4.5 V

b

c

e


41


Title: Temperature Controlled Switch

Aim: To observe and describe the operation of a simple transistor switching circuit controlled by temperature.

Apparatus: 4.5V battery, potential divider (board 70), thermistor, 4.7k variable resistor, transistor switch/indicator (board 41), alpha links, connecting leads.

Block Diagram


(containing thermistor)

Transistor

Switch

Output Device

Circuit Diagram

Instructions:

Set up the circuit as shown. Adjust the variable resistor until the LED is off (just). Heat the thermistor and watch what happens to the LED. Describe the operation of the circuit at each stage (input,

process, and output). Suggest a use for this circuit. Redesign the circuit so that the thermistor turns off when it is

cold.

0 V

4.5 V

b

c

e


42


Title: Time Delay Switch

Aim: To observe and describe the operation of a simple transistor switching circuit controlled by a time delay circuit.

Apparatus: 4.5V battery, potential divider (board 70), 1000µF capacitor, resistor, 4.7k variable resistor, transistor switch/indicator (board 41), component investigation board, push switch, alpha links, connecting leads

Block Diagram


(containing capacitor)

Transistor

Switch

Output Device

Circuit Diagram

Instructions:

Set up the circuit as shown. Press the push switch to discharge the capacitor. Watch what happens to the LED. Describe the operation of the circuit at each stage (input,

process, and output). Suggest a use for this circuit.

0 V

4.5 V

b

c

e


43


Title: Power Ratings

Aim: To determine the power ratings of electrical appliances and calculate their energy consumption when in use.

Apparatus: 5 electrical appliances showing their ratings plate.

Electrical appliances have a power rating which is shown on their ratings plate. This power rating is the energy used (transformed) per unit of time. From this definition we get the formula P = E/t. Power is measured in watts (W) which is equivalent to 1 joule/second (Js-1).

Instructions:

Note the power rating for each of the appliances.

Use the formula P = E/t to calculate the amount of energy used by the appliance if it was in use for 30 seconds, 5 minutes, and 2 hours.

What two factors affect the electrical energy used by the appliance?


44


Title: Power, Current, and Voltage

Aim: To determine the relationship between power, current, and voltage.

Apparatus: Variable low voltage d.c. power supply, 2 multimeters, 3 lamps (24W, 36W, and 48W).

The power rating of an appliance can be determined by measuring the current through it and voltage across it when it is in use.

Instructions:


Lamp Power Rating (W)

Voltage across lamp (V)

Current through lamp (A)

Current x Voltage

24 12

36 12 48 12

Set the power supply to zero. Set up the circuit shown in the diagram using the 24W lamp. Switch on the power supply. Increase the supply voltage until the voltage across the lamp

reads 12V. Record the current through the lamp. Repeat using the 36W then 48W lamp. Complete the last column of the table. Conclude the relationship for power, current, and voltage.

- +

A

V


45


Title: Combining Equations

Aim: To explain the equivalence of power in terms of potential difference, current, and resistance.

Apparatus: None.

In Physics it is possible to combine equations to create new ones. In this activity you will combine P = IV and V = IR to generate two new equation P = V2/R and P = I2R. Follow the two sets of instruction below.

Instructions:

To generate P = I2R

Start with P= IV

Replace the V in P = IV with IR (since V = IR)

Square the I (since you have I x I)

To generate P = V2/R

Start with P= IV

Replace the I in P = IV with V/R (since I = V/R)

Square the V (since you have V x V)

Documents

Activity Booklet - eduBuzz.org · 2014. 10. 7. · These coils are called field or stationary coils and are fixed in the casing to form the stator. If the coils are stationary, then