Exam Tonight, 7:30 PM, Muenzinger Psychology E-0046 Bring calculator, pencils, and note cards (two 3x5 cards) About the Exam: Format same as Exam 1: Part

Exam Tonight, 7:30 PM, Muenzinger Psychology E-0046

Bring calculator, pencils, and note cards (two 3x5 cards)

About the Exam:

• Format same as Exam 1: Part multiple choice, part essay

• Exam focuses on material covered since Exam 1, but you should review previous material since we have been building on physics from beginning of semester.

• best preparation- go over homework and solutions, also class notes (particularly questions in class), and be sure you understand answers.

• Note Cards: good way to study is to make list of most important ideas and formulas needed.

• Homeworks to focus on: Sound Waves, Circuits (Audio Amplifiers and Diodes), TVs, Sunlight and Color

GRID

CATHODE: heated a bunch, boil off electrons … so now free in vacuum tube.

ANODE, high voltage, lots of excess positives

TV … Create beam of electrons accelerating towards screen. Hit screen, excite phosphor, create light.

PhosphorCoatingAccelerating

Anode, lots of excess positives +

+ + + + + + + + + + +

Each electron hits screen creates a photon of light. Grid controls number of electrons in beam. How and why?

a. Add a bunch of excess negative charges on grid. Electrons trying to escape pushed back inside.

b. Add a current through grid to create magnetic field. Electrons trying to escape pushed back inside.

c. Add a bunch of excess positive charges on grid. Electrons sucked up by grid.

Big V

GRID

CATHODE: heated a bunch, boil off electrons … so now free in vacuum tube.

ANODE, high voltage, lots of excess positives


PhosphorCoatingAccelerating

Anode, lots of excess positives +

+ + + + + + + + + + +

Answer is a. Add bunch of negatives to grid! Pushes electrons back towards cathode … fewer into beam.

Control where beam hits screen with magnetic fields!

-- - - --- - -

TV’s…. Some questions on interaction of magnetic fields and electrons

N

S

Permanent Bar magnet

Review Magnetic Field Lines –Magnetic field lines for Bar Magnet

A

How does the magnetic field interact with electrons and other magnets?

a. A stationary electron placed at point A will move down.

b. A stationary electron placed at point A will move to the right.

c. A small bar magnet place at A will rotate to line up with the magnetic field

d. Both a and ce. Both b and c

Answer is c only.

N

S

Magnetic field line points in direction of force on a North Pole. So at A, north pole feels force down, south pole feels force up. No force on stationary electrons! Magnetic fields only put forces on MOVING electrons, as in electron beams in TVs.(Why? … Because that’s how nature works … we observe, describe observations.)

Forces on moving electrons by magnetic fields:

An electron is moving at speed V through a uniform magnetic field. In which case is the force exerted by the magnetic field on the moving electron greatest? A) B) C)

D) The electrons in A, B, and C all experience the same size force because the magnetic field is the same strength in all cases. E) Constant magnetic fields cannot exert forces on charges.

Ve-

V

e-

Ve-

Greatest force Some force, part

of velocity is perpendicular to magnetic field

No force on electron, velocity is NOT AT ALL perpendicular to magnetic field

Correct answer is A.Amount of force on electron depends on how perpendicular velocity is to magnetic field.

Ve-

Force

Magnetic field

ElectronVelocity

GRID


PhosphorCoating

+ + + + + + + + + + + +

DeflectingCoils (A)

DeflectingCoils (B)

TV’s…. Some questions on interaction of magnetic fields and moving electrons

N

S

Can you create a steady magnetic field with a coil of wire?

a. Sure, Spin coil or move coil up and down rapidlyb. Sure, Send steady current through coilc. Sure, Send steadily changing current through coild. No, It is not possible

Answer is B. Steady current produces steady magnetic field. (Remember creating electromagnet in lab.. Picking up washers.

Larger current, stronger magnetic fieldSmaller current, weaker magnetic fieldNo current, no magnetic field

Reverse current, magnetic field in opposite direction …

N

S

GRID


PhosphorCoating

+ + + + + + + + + + + +

DeflectingCoils (A)

DeflectingCoils (B)

Current through Coils A(same current, same direction, through both)

Vertical magnetic field. Beam deflected horizontally

Periodic oscillations in the electric field.

Travels away from source at the speed of light (c = 3 x 108 m/s)

Source

e-

Electromagnetic Radiation Review: Generated by accelerating charged particles…

oscillating electrons in a TV antenna or oscillating electrons at the surface of the sun.

Wave of changing electric field … electric field puts force on an electron (and magnetic field) traveling away from source. Characterized by a wavelength and frequency.

What do radio waves and uv light have in common? a. Both are propagating waves of changing electric field. b. Both travel at the speed of light through spacec. Both are generated by accelerating charged particlesd. All of the above

Periodic oscillations in the electric field.

Travels away from source at the speed of light (c = 3 x 108 m/s)

Source

e-

Electromagnetic Radiation Review:

Generated by accelerating charged particles…oscillating electrons in a TV antenna or oscillating electrons at the surface of the sun.

Wave of changing electric field (and magnetic field) traveling away from source. Characterized by a wavelength and frequency.

What do radio waves and uv light have in common? d. All of the above. These are characteristics common to all forms of electromagnetic

radiation (Radio Waves, Microwaves, Infrared (heat), Visible light, UV light, X-rays, Gamma rays).

What is different between these forms of EM radiation?

Wavelength. Frequency. Amount of energy per packet of radiation (photon).

Which of the following statements are true: 1. All EM (electromagnetic) radiation comes in small packets called photons.

2. Every blue photon has the same amount of energy as every other photon of that exact same blue color.

3. It is possible for a red photon to have the same amount of energy as a blue photon.

4. If I measure the energy of the red light emitted by a red LED, it is possible to measure any amount energy 0 J and higher.

a. 1 b. 1 and 2 c. 1 and 3 d. 1, 2, and 4 e. 1, 3, and 4

Which of the following statements are true: 1. All EM (electromagnetic) radiation comes in small packets called photons.

True: A photon is a unit of light energy. Can have one photon, two photons, etc. Cannot have 1.5 photons of red light.

2. Every blue photon has the same amount of energy as every other blue photon.True: A photon of a specific color of light has a specific energy. All photons of that exact color of light will have that same amount of energy… no more, no less.

3. It is possible for a red photon to have the same amount of energy as a blue photon. False: For each frequency of electromagnetic radiation (Radio waves, Microwaves, visible, UV), the energy in a photon of EM radiation at that frequency is different. This energy is given by Energy of photon = Planck’s constant x frequency = 6.626x10^-34 x frequencySpeed of light = frequency x wavelength

4. If I measure the energy of the red light emitted by a red LED, it is possible to measure any amount energy from 0 Joules and higher. False: Detect one photon of energy, two photons, three photons, 1,000,000 photons, but never 1,000,000.1 photons.

a. 1 b. 1 and 2 c. 1 and 3 d. 1, 2, and 4 e. 1, 3, and 4

White paint has little particles of transparent material in it to make paint look white. The main reason this works is because:

a. They add texture to the surface it is not smoothb. They each reflect little bit of light because speed of light in

particles is slower than in base material of paint. c. They each reflect all of the light that hits them, but

oriented in different directions so on average wall looks white.

d. Little particles have no function. magnify

Answer is b. Light changes speed going into particles… a little bit of light reflects off each particle, enough particle in paint to reflect all the light. Any light not reflected is absorbed (dye absorbs light). Energy turns into heat!

Ground

Gate

+9V Power Source

B

A

C D

E

S N

PermanentMagnet

50 OhmResistor

Circuits: understand where electrons are flowing and why.

Components: Resistors, Transistors, Capacitors, Diodes

Audio Amplifier

+ -

NP

ElectronFlow

Diode: Joined P-Type and N-type semiconductor

Gate

LED

Diode Review:• Pass current in only one direction.• Junction of P doped and N doped semiconductors

empty

full

Pure Semiconductor

Si, 4 electrons go intovalence band, just fill

empty

full

N-type semiconductor

Mostly Silicon w/tiny fraction Phosphorus

P-type semiconductor

Mostly Silicon w/tiny fraction Boron

1 empty level per boron atom

empty

full

What is required for material to be a good conductor? a. A small energy gap between the bandsb. A band that is completely full of electrons so a lot of electrons can flowc. Empty energy levels very, very close in energy to the highest energy electrons

Diode Review:• Pass current in only one direction.• Junction of P doped and N doped semiconductors

empty

full

Pure Semiconductor

Si, 4 electrons go intovalence band, just fill

empty

full

N-type semiconductor

Mostly Silicon w/tiny fraction Phosphorus

P-type semiconductor

Mostly Silicon w/tiny fraction Boron

1 empty level per boron atom

empty

full

What is required for material to be a good conductor? Answer is c. Empty energy levels very, very close in energy to the highest energy

electrons. Both N-type and P-type semiconductors satisfy this requirement.

Diode Review:• Electrons flow N to P only. One direction.

N-type

empty

full

P-type

empty

full

Electrons can flow from N-type to P-type

To

+Voltage

In other direction, voltage can’t give electrons enough energy to jump band gap so current does not flow.

Light emitting diode. One photon with each electron that passes across P, N junction.If current is steady, bigger energy gap between bands will mean: a. brighter light , b. dimmer lightc. different color lightd . Both a and c. e. both b and c.

Important things to keep in mind about circuits:

Electrons always want to flow from lower voltage to higher voltage (towards excess positive charge).

Rate of electron flow (current) from lower to higher voltage depends on resistance between these two points

Electrons are attracted to excess positive charge

Electrons will repel each other (like charges repel)

If both of these then force of attraction to positives will balance force of repelling of each other, else electrons will move (flow).

If no voltage difference, no reason for electrons to flow

GROUND

(0 V)

+9 V

R1 = 50 Ohms

R2 = 50 Ohms

B

Voltage, Current, and Resistance

What if R2 decreases, what changes? a. Current increases, Voltage diff. across R1 increases,

and Voltage at B is lowerb. Current decreases, Voltage diff. across R1 decreases,

Voltage at B is higherc. Current increases, Voltage diff. across R1 increases,

and Voltage at B is higherd. Current decreases, Voltage diff. across R1 decreases,

Voltage at B is lower

If R1 and R2 are both 50 ohms, then voltage at B is 4.5 Volts… electrons have used up half of their 9 Volts of energy by the time they get to B

GROUND

(0 V)

+9 VR1 = 50 Ohms

R2

B

Voltage, Current, and ResistanceIf R2 decreases, what changes? a. Current increases because total

resistance of path is lower!(Rtotal = R1 + R2). Rtotal less. V=IR so I = Vtotal/Rtotal ; Vtotal = 9V.

With larger current, Voltage Diff across R1 increases. (each electron loses more energy lost across R1 now.) V_across R1 = IR.

If more voltage is lost across R1, Voltage at B decreases

Gate

NO Charge at GateCurrent valve closedInfinite ResistanceI=0

A

Transistors control current flow by changing resistance:Control current by varying amount of positive charge at Gate (A)

Gate

Lots of positive charge at GateCurrent Valve OpenSmall ResistanceI is big

A

++

+

I

Adjust positive charge on Gate to get current in between I = 0 and I = big

NOTE: No current or electron flow across here. There is an insulator there.

GROUND

(0 V)

+9 VR1 = 50 Ohms

R2

B

Voltage, Current, and Resistance

Adding more positive charge to Transistor’s Gate is like lowering resistance of R2. Effect is increase current and lower voltage at B.

Gate

A+

What voltages are possible at B? a. any voltageb. any voltage greater than 0 Vc. 0 to 20 Vd. 0 to 9 Ve. 1 to 8 V

Answer is d. 0 to 9 V. 0 V if transistor is wide open… no resistance from transistor and current limited by R1. 9 V if transistor resistance is infinite… no current flow at all.

GROUND(0 V)

Capacitors – two metal plates that store charge; insulator in between plates.

No current or electron flow across here.

Adjustable Power Supply

+9V “Above Ground”

GROUND(0 V)

Capacitor Review:

++

++

++

++

++

++

++

- - - - - - -- - - - - - -

+9V



- - - -

- -

- -

-

-

-

-

- - - -

A B

What happens when I close the switch what happens to the bulb? a. Bulb turns on and stays at constant brightness until open switch again. b. Bulb turns on, dims steadily, then is off.c. Bulb turns on and has steady brightness until off. d. Bulb does not light, no current because no complete circuit.

GROUND(0 V)

Capacitor Review:

++

++

++

++

++

++

++

- - - - - - -- - - - - - -

+9V



A B

What happens when I close the switch? b. Electrons flow for brief period of time and then stop. Current slows as voltage difference between capacitor plate and ground decreases. (V = IR ; I =V/R) Current stops when no voltage difference between capacitor plate A and positive terminal of power supply (both at +9 V) and no voltage difference between capacitor plate B and Ground. (both at 0 V)

0 V

time after voltagehooked up.

0

Cu

rren

t

- - - -

GROUND

Capacitor Review:

++

++

++

++

++

++

++

- - - - - - -- - - - - - -

+9V +0V


+9V “Above Ground”- - - -

-

-

-

-

- -

- -

1) Lower Voltage of Power Supply

2) Plate A is at higher voltage than Supply. Electrons flow towards Plate A until voltage difference is 0. Excess positive charge on Plate A will decrease.

3) Attraction of electrons on Plate B to positive charge on Plate A has decreased. Force of electrons repelling each other is greater than attraction to Plate A, so some electrons leave … flow back to Ground.

A B


+4V

Documents

Exam Tonight, 7:30 PM, Muenzinger Psychology E-0046 Bring calculator, pencils, and note cards (two 3x5 cards) About the Exam: Format same as Exam 1: Part