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142 Final Flashcards

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1
Q

Conductors

A

at least some of the charges are free to move around within the material

ex: metals, ions in water

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2
Q

Insulators

A

charges do not move freely

ex: plain water, wood, plastic, glass

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3
Q

Charging by conduction

A

actually touch the charged object to neutral object

charge is free to move from the conductor to the object

neutral object will have the same charge as the charged conductor brought near

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4
Q

Charging by induction

A

bring charged material towards a neutral object

like charges in neutral object will repel

attach a wire to ground, like charges will leave

neutral object becomes charged the opposite of the charged insulator brought near

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5
Q

What happens if you move the insulator away from neutral object before disconnecting ground wire?

A

The ground wire will push charges back into the object to make it neutral

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6
Q

Why is net charge inside conductors 0?

A

charges move around and adjust to make sure the net electric field is 0

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7
Q

If you release a particle from rest in what direction will it move?

A

towards decreasing potential energy

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8
Q

For potential energy graphs, what trick helps draw them?

A

use the charges when calculating potential energy

tells you +y or -y

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9
Q

What happens to electric potential when distance decreases for a positive charge?

A

when r decreases, V increases

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10
Q

What happens to electric potential when distance decreases for a negative charge?

A

when r decreases, V decreases

V becomes more negative

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11
Q

What direction does a + charge move in a battery?

A

From - to +

Against the E field, which is unnatural

Does this through a chemical reaction

*only applies to batteries not capacitors

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12
Q

Why can we normally ignore internal resistance of a battery? And what can we do when we do?

A

Can normally ignore because r«

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13
Q

Why is voltage difference across battery actually lower than EMF?

A

internal resistance

∆V=E(1-r/r+R)

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14
Q

What happens to current across a capacitor as voltage increases?

A

current decreases

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15
Q

What can not change instantly on a capacitor?

A

charge / voltage

Q=cV

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16
Q

What can not change instantly on an inductor?

A

current

voltage can (rate of change)

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17
Q

If you wait a long time after closing a capacitor what always happens to CURRENT?

A

current goes to 0

*check rules but this should work

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18
Q

How can you treat a capacitor if it has no charge the moment when you open / close a switch?

A

can treat the capacitor as a wire and find the current through it

since V=0 (can’t change), the capacitor is basically a current carrying wire

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19
Q

What would happen to an inductor if you changed the current through a circuit?

A

you could produce an induced emf in the inductor (like a solenoid)

emf would be in the direction that opposes the created B-field (if increasing B magnitude)

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20
Q

How can you treat the inductor after a long time?

A

the current is no longer changing, so there is no voltage across the inductor

can treat as a wire

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21
Q

What is the magnetic force between two parallel wires with current in the same direction?

A

attractive

22
Q

What is the magnetic force between two parallel wires with current in opposite directions?

A

repulsive

23
Q

What do you have to make sure to do for AC circuits?

A

make sure calculator is in radians when using sin functio

24
Q

AC circuits: relationship between current and voltage across resistors

A

current and voltage are in phase

V=IR

when current increases, so does voltage

25
Q

What is rms?

A

a type of average

26
Q

AC circuits: relationship between current and voltage in capacitors

A

voltage can’t change instantly

the current leads the voltage

27
Q

AC circuits: relationship between current and voltage in inductors

A

current can’t change instantly

the current lags the voltage

28
Q

What does Xc stand for?

A

capacitive reactance

has units of olmns

29
Q

Transformers general premise

A

when current changes in one wire, the other wire gets an induced current

30
Q

Why do transformers not work in DC circuits?

A

the current is not changing to create an induced current

31
Q

When just have Fb acting on a velocity, not completely perpendicular, what is the motion of the particle?

A

only the perpendicular component gets acted on

the parallel component does’t do anything and just moves at a constant speed

gives us a spiral with a constant pitch

32
Q

When have Fb and Fe acting on a particle what shape do you get?

A

spiral with a non-constant pitch

33
Q

Back current

A

current change by flipping switch creates its own B (from current), thus has a ∆I and an EMF

want to oppose the current’s B field, so create an induced current in the opposite direction

34
Q

What happens to back current over time?

A

no back current since nothing is changing to induce current

35
Q

What is the angle used for flux?

A

the angle between the “A” vector (perpendicular to the surface) and B

36
Q

How to find the direction of the “A” vector for torque problems? For example, between into and out of the page?

A

Have to use the direction of the current and the right hand rule

37
Q

How to find the direction of torque?

A

use the RHR with the “A” vector and B field

38
Q

What is something to be careful of when using wavelength?

A

often need to convert nanometers to meters in problems

39
Q

What direction do + charges feel an electric force?

A

feel a force in same direction as E field

40
Q

What direction do - charges feel an electric force?

A

feel a force in opposite direction as E field

41
Q

When light is perfectly polarized from Brewster’s angle what direction is the E field?

A

the E field goes in and out of the page (perpendicular to the v)

is parallel to the surface that the light reflected off of

42
Q

What is strategy for doing circuit problems?

A

take picture on iPad

highlight and look to see if anything is in parallel or series

simplify the circuit

43
Q

What is strategy for inductor problems?

A

always see what the current is through the inductor before a change happenns!

44
Q

When the question says magnitude what should you give?

A

a positive answer

45
Q

When can you use a screen to see an image? Why can’t you see the image without the screen?

A

use a screen to see an image if the virtual image is real (where the light is)

can’t see the image without the screen because the light rays that make the image are going away from you

46
Q

If a negative charge moves from 0V to +V do you have to put energy into the system to slow the particle or take energy out of the system to slow the particle?

A

as the negative particle moves to a higher V, PE is decreasing

this is because higher V is more negative, so smaller PE

then, as PE decreases KE increases. So, to slow the particle you would have to take KE out of the system

47
Q

Positive work

A

put energy into the system

48
Q

negative work

A

take energy out of the system

49
Q

How can you tell if a capacitor is at negative or positive V based on motion of particle released close to a capacitor?

A

particle will move to a lower PE

if a positive charge moves away, it is moving towards 0V which means capacitor was at + V

if a positive charge moves towards, it is moving towards - V from 0 V to have a decreasing PE

50
Q

How do you find voltage at a point between the two plates of the capacitor?

A

find the voltage drop across the capacitor and the starting / final voltages

at the certain point, the particle has performed a ratio of the voltage drop

Vpoint = Vstarting - (ratio traveled / distance between plates)Vdrop

Physics (7 decks)

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