Electrical Energy in the Home

Electrical Energy in the Home

Society has become increasing dependent on electricity over the last 200 years

1.1 Discuss how the main sources of domestic energy have changed over time

First main sources of domestic energy was wood then animals, wind and water and then fuels like coal, gas and oil

1.2 Assess some of the impacts of changes in, and increased access to, sources of energy for a community

Pollution Increases standard of living Lighting and heat More demand for products Effects the environment Greater freedoms Greater access to communication devices1.3 Discuss some ways in which electricity can be provided in remote locations Generators Solar Wind Geothermal Wave/water HumanOne of the main advantages of electricity is that is can be moved with comparative ease from one place to another through electric circuits

2.1 Describe the behaviour of electrostatic charges and the properties of the fields associated with them

Electric charge is when a electron and protons exert a force on one another Like Charges Repel, Unlike Charges Attract Excess electrons = negative charge Excess protons = positive charge The charge from this is an electrostatic charge2.2:Define the unit of electric charge as the coulomb

Coulomb is the SI unit for electric charges Is the amount of electric charge passing through a point every second when a current of one AMP through that point 1C = 1 AMP/ second IC = 6.2x10 6 ^ -19 Micro Coulombs = UC2.3:Define the electric field as a field of force with a field strength equal to the force per unit charge at that point An electric field is a region around an electrically charged object where a positively charged object will experience a force The force on a charge is proportional to the electrical field strength (E) at that point and the charge placed in the electrical field (q) Direction is the direction the force would act on a positively charge placed in the field A negative charge force is in the opposite direction to the field SI Unit: Newtons/Coulombs (NC^-1)2.4:Define electric current as the rate at which charge flows (coulombs/second or amperes) under the influence of an electric field

Electric Current is the rate at which charge flows under the influence of an electric field. Moving charges are called charge carriers Conventional current moves from positive to negative while electron movement is in the opposite direction but the flow of electrons is negative to positive Electrical currents flow in the direction of the electric field

2.5:Identify that current can be either direct with net flow of charge carriers moving in one direction or alternating with the charge carriers moving backwards and forwards periodically Direct Current:involves the net movement of charge carriers (electrons)

along a conductor. The electrons move in the opposite

direction to the direction of the electric field Alternating:involves the oscillation of electrons due to an electric

field constantly changing direction e.g. generators2.6:Describe electrical Potential Difference (Voltage) between two points as the points change in potential energy per unit charge moving from onepoint to the other (joules / Coulomb or volts)

The potential Difference across the power supply is the potential rise across the power supply.

The potential drop is the potential difference across a resistor

Potential difference is the work done per unit charge and is expressed as joules / coulomb

V = W Q2.7:Discuss how potential difference changes between different points around a DC circuit

The potential difference across the power supply is equal to the sum of the potential difference across the resistors in a series circuit

The potential difference in a parallel circuit is the same as the potential difference across the power supply2.8:Identify the difference between conductors and insulators

A conductor is a material which contains charge carriers and allow particles to move through them

An insulator is a material containing no charge carriers and dont allow movement of charged particles R =V

I

2.9:Define resistance as the ratio of voltage to current for a particular conductor

The resistance of a resistor is the potential difference across the resistor divided by the current passing through the resistor A resistor is an electrical component that limits or reduces current flow. The unit for resistance is Ohms Resistors that obey Ohms law are called Ohmic resistors, their graph of V vs. I will be a straight line where gradient = their constant resistance.

2.10:Describe qualitatively how each of the following affects the movement of electricity through a conductor

Length: The longer the wire is, the greater the chance of a collision between the free electron and an ion in the lattice. Hence, the longer a wire the greater the resistance

Cross sectional area: The Smaller the area of the cross-section of the wire, the greater the chance of a collision with an ion in the lattice, hence the smaller the area of the cross section, the greater the resistance.

Temperature: The higher the temperature of a conductor, the greater the resistance because when the temp is higher the ions in the lattice vibrate with greater amplitude, increasing the chance of a collision between a free electron and an ion in the lattice. Material: When a free electron is drifting through a wire, the chance of collision with an ion in a lattice depends on what material the wire is made of. Materials with a lower resistance are better conductors.

2.11:Identify materials that are commonly used as conductors to provide household electricity

Copper: is mainly used due to the fact that it hosts little resistance (i.e. is a good conductor) and does not carry high currents therefore is safer in terms of an overload.

Silver: is occasionally used in some high quality electronic equipment due to its higher conductivity but it is not used widely due to its high price.

Aluminium: is not as good a conductor as silver or copper but it is used in the wires for overhead power line distribution because of its light weight. The light weight allows the supporting structures to be placed further apart and this reduces the overall cost.

Series and Parallel circuits serve different purposes in households

3.1:Identify the difference between series and parallel circuits

3.2:Compare parallel and series circuits in terms of voltage across components and current through themSeries:

Circuit connected end to end with only one possible path

Each resistor carries the same current regardless of the resistor value and this current value equal to the current supplied to that part of the circuit

Each resistor in series has its own voltage drop and the sum of the voltage drops equals the voltage supplied

Parallel:

A parallel circuit is a closed circuit in which the current divides intotwo or more paths before recombining to complete the circuit.

Each resistor in parallel has its own current and the sum of the currentvalues equals the current supplied. Each resistor in parallel has the same voltage drop regardless of theresistor value and the voltage drop in each parallel resistor equals thevoltage supplied.

3.3:Identify uses of ammeters and voltmeters 3.4:Explain why ammeters and voltmeters are connected differently in a circuit

Ammeter:

An ammeter is a device used to measure the current in an electrical circuit (measured in amperes or amps). Ammeters are placed in series in a circuit because they measure the rate at which charge flows, which does not decrease as it passes through a resistor.

Voltmeter:

A voltmeter is a device used to measure the potential difference acrossa component or components across a circuit (measures in volts). A voltmeter is placed in parallel to the component which we arerequired to measure the potential difference across, because avoltmeter measures the difference in potential energy. This is the potential energy before the component minus the potentialenergy after the component which is the potential difference.3.5:Explain why there are difficult circuits for lighting, heating and other appliances in a house There are different circuits for lighting, heating and other appliances because:a) Each circuit is designed to carry a certain maximum current and it varies amongst the circuits based on the requirements for individual appliances. Exerting the maximum current could cause a circuit overload, which can lead to a fire.b) The amount of current that passes through also influences the wires needed. For circuits that require more current require larger wires, so the resistance decreases, which decreases the heat generated. This means that there is a lower chance of a fire.c) Also, separate circuits are used to decrease the chance of short circuitsThe Amount of Power is related to the rate at which Energy is transformed

4.1:Explain that power rate at which energy is transformed from one form to another.

Power: the rate which energy is transformed from one form to another, or the rate energy is supplied to a device Energy = joules Time = seconds Power = joules/sec or watts P = IV

P = Power I = Current V = Voltage4.2:Identify the relationship between power potential difference and current

The current is I amps, therefore I coulombs of charge pass through the resistor in one second. Each coulomb of charge passing through the resistor dissipates V joules of electric potential energy. Therefore, in one second, VI joules of electric energy are dissipated. Power dissipated in a resistor is the number of joules of energy dissipated in one second The relationship between work and voltage is shown below W =qV

Substituting qV in to the work time formula you get. P = qV/t

But I = q/t

Hence P = IV

Q = potential energy

Power is the product of the voltage across the device and the current flowing through it.4.3:Identify the total amount of energy used depends on the length of time, the amount current is flowing and be calculated using energy = VIT

The total amount of energy depends on time and the amount of current

E = VIT E = Energy

V = Voltage

I = Current

T = Time

4.4:Explain why the kilowatt hour is used to measure electrical energy consumption rather than the joule

Kilowatts are used due to large amount of electricity used One Kilowatt hour can be defined as the amount of energy used by a one kilowatt device in one hour. Energy in Kilo hours = power in kilowatts x time in hours W = PtElectric Currents also produce magnetic fields and these fields are used in different devices in the home

5.1:Describe the behaviour of the magnetic poles of bar magnets when they are brought close together

When to magnetic poles are together, they exert a force on each other

Two of the same poles repel each other

A North and a South pole attract each other

Like poles repel each other, opposite poles attract each other

Closer = stronger the force of attraction or repulsion

There will be four different pairs of forces between the poles resulting with either attraction or repulsion A pair with equal and opposite magnetic poles is called a magnetic dipole

5.2:define the direction of the magnetic field at a point as the direction of force on a very small north magnetic pole when placed at that point

The direction of a magnetic field is given by the direction of the force on the North Pole of a compass needle when placed at that point in the magnetic field.

5.3:describe the magnetic field around pairs of magnetic poles Magnetic fields, B. Magnetic fields are measure in Teslas, T.

5.4:describe the production of a magnetic field by an electric current in a straight current carrying conductor and describe how the right hand grip rule can determine the direction of current and field lines

When current is passed through a conductor, a magnetic field is created around it. The direction of the magnetic field can be found using the right hand rule. Point your right hand thumb in the direction of the current and the direction of your fingers is the direction of the magnetic field.

5.5: Compare the nature and generation of magnetic fields by solenoids and a bar magnet

A solenoid is a coil of insulated wire of many turns. It is long compared to its diameter. A current through the solenoid will produce a magnetic field and the direction of the field can be determined by the solenoid rule. Grip the solenoid with the fingers wrapped around the solenoid pointing in the direction of the current. The thumb will point to the north pole of the solenoid. The lines of magnetic flux are continuous and the direction of the magnetic field is from north to south outside the solenoid but from south to north inside the solenoid. When a current flows into the Solenoid it produces a magnetic field around the coil which is similar to that of a bar magnet. Frenchman Ampere stated that as the solenoids field arose as a result of a current, then the field of a bar magnet must also be due to tiny current loops in the bar.

5.8:identify data sources, gather, process and analyse information to explain one application of magnetic fields in household appliances

Inside a speaker, the voice coil is an electromagnet (a long coil of wire that is wrapped around a piece of magnetic metal such as iron). When current is passed through the coil, a magnetic field is created around the coil and magnetizing the metal which it is wrapped around.

the magnetic field around the electromagnet can alter the orientation of the pole, hence constantly reversing the flow of electricity. This means that the electrons also, keep alternating direction.

The permanent magnet under the voice coil interacts with the electromagnet. When there is current passing through the electromagnet, it alternates direction many times per second. The positive end of the electromagnet is attracted to the negative pole of the permanent magnet, but when the polar orientation of the electromagnet switches, so too does the direction of repulsion and attraction. This pushes the voice coil back and forward like a piston, which vibrates the air in front of the speaker, creating sound waves. The speed at which the coil vibrates changes the frequency and the amplitude of the wave produced by the diaphragm.

Safety devices are important in household circuits

6.1:Discuss the dangers of an electrical shock from both a 240 volt AC mains supply and varies DC voltages, from appliances on the Muscles of the body An electric shock or electrocution occurs when a large current passes through the body. This current depending on the strength will cause a disturbance of the nervous system why will often produce effects on the muscles of the body, or in more severe cases cause death (often due to heart failure). In the house hold an electric shock will often occur when a person comes into contact with a live wire and the earth (a connection is made between the live wire and the earth with the person in between acting as a wire). The Effect of DC voltages: An electric current passed through the body can cause muscles to contract. This may seem harmless but if the muscles for example used in breathing are involved affects can be disastrous, Often the occupant will be unable to breath and may cause death due to lack of oxygen to the brain The effect of AC voltages

6.2 - Describe the Functions of circuit breakers, fuses, earthing, double insulation and other safety devices

In household circuits a number of safety methods are employed to ensure the occupants safety: -Double Insulation: In a household all wires a required to be covered by an electrical insulator i.e. PVC, however some appliances such as electric shavers which are often very close to water have double insulation both on the inside and outside of the device. This safety measure is put into place so that the user is protected in a case where the inner insulation fails. -Fuses: Fuses are used to prevent overloading of household circuits. A fuse is effectively a resistor with a very low melting point it is inserted in the household circuit in a series. If the resistance gets two high the fuse melts and the circuit is broken. This technique is employed to prevent the wires running through the house from heating up excessively and setting the house of fire.

-Circuit Breakers: Circuit breakers essentially have the same function as a fuse but instead of melting when the current is high, a electromagnet breaks the circuit, the advantage of a circuit breaker is that it can be reset. -Earth Wire: An earth wires function is to provide protection to the occupants of a household from electric shock when using an appliance. When household wiring is installed, a good conductor is used to connect the fuse box to the earth. At the fuse box the wire corning from the earth is (a) connected to the neutral wire from the electricity supply and (b) connected to earth wires that go from the fuse box to each power outlet. Power outlets have three wires connected to them from the fuse box the; active wire, the neutral wire and the earth wire

Most appliances are connected to the powder outlet by a three-point plug, connected to a lead containing three wires which continue the active, neutral and earth wires to the appliance.

The active and neutral wires provide power to the appliance. The earth wire is connected to the casing of the appliance. The earth wire provides protection in case the active wire comes in contact with the casing of the' appliance unless has double insulation

-Residual Current Device: A residual current device (RCD) detects any leakage of current to the earth either through your body or through some other conductor. It is designed to switch off the current very quickly before it reaches a harmful level. Sometimes an RCD is called a safety switch. An RCD reduces the risk of electric shock. (However it will not protect you in all instances.) An RCD must be installed as standard fuse-box equipment in all new houses and buildings.

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Parallel Circuit

Series Circuit

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