Electric Fields

Question 1

What if one of the charges becomes negative

Answer 1

Question 2

Define electric field

Answer 2

An electric fields a region where a charge experiences a force

Question 3

What charge does field lines show the direction for

Answer 3

Question 4

For negative and positive charges what way do the field lines act towards the charged particle

Answer 4

Question 5

Draw field lines for when a positive and negative charged particle meet
Also draw on equipotential

Answer 5

Question 6

Draw field lines and equipotential for two identical point charges

Answer 6

Question 7

Draw field lines for two uniform parallel plates

Answer 7

Question 8

Between L & M, state which one has a greater magnitude of charge and explain your answer

Answer 8

L as it has more field lines coming out of it and it’s field lines are closer together

Question 9

A student suggest that this is a gravitational field. Explain why it isn’t

Answer 9

Is not because in a gravitational field lines do not act away from the particle but here they act away from L

Question 10

Define coulomb’s law of attraction

Answer 10

Force between two point charges is directly proportional to the product of their charges and inversely proportional to the square of their seperation

Question 11

Answer 11

Question 12

Define an electric field strength and what direction does it act

Answer 12

Electric field strength is the force per unit charge that would experience a small positive test charge
Acts away from positive charge and towards negative charge

Question 13

Draw graph for electric field strength against radius for a radial field

Answer 13

Question 15

Define absolute electric potential energy
Give equation for absolute electric potential energy
Should you keep signs of charge when calculating potential energy

Answer 15

Work done in moving a charged object from infinity to that point in the electric field
Yes you should keep the sign as you can have either a positive or negative potential energy

Question 16

Answer 16

Question 17

What is a capacitor
And then give it’s definition

Answer 17

Question 18

Process of capacitors when added to a circuit

Answer 18

Question 19

In the equation C = Q/V, what always remains constant for a capacitor

Answer 19

Capacitance remains constant so charge is directly proportional to potential difference

Question 20

How does a dielectric work

Answer 20

Question 21

Define the time constant

Answer 21

Time contact is time in seconds it takes for charge to fall to 1/e of its original value

Question 22

Equation for charging and discharging a capacitor
Use charge

Answer 22

Charging Q=Q0 (1-e^-t/RC)
Discharging Q=Q0e^-t/RC

Question 23

Draw graphs for charging capacitor

Answer 23

As current is same for discharge you still use the equation I=I0e^-t/RC

Question 24

Take natural logs for discharging equations, use charge as an example

Answer 24

Question 25

Answer 25

Question 26

Answer 26

B

Question 27

True or false, Capacitance of a capacitor is amount of energy stored by capacitor when pd across plates is 1V

Answer 27

True

Question 28

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Question 29

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Question 30

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Question 31

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Question 32

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Question 33

Answer 33

A

Question 34

Answer 34

D

Question 35

State how initial charge could be obtained from a graph of current against time

Answer 35

Determine area under the graph

Question 36

Only do part ii)

Answer 36

Energy is lost through heating of wires or motor Energy is lost in overcoming frictional forces in the motor Capacitor will not drive motor when voltage becomes low

Question 37

C) Explain why there is an increase in energy stored by capacitor when polythene sheet is pulled out between the played

Answer 37

C) in polar dielectric molecules align in field with positive charged end towards negative plate Work is done on capacitor seperating the positively charged surface of dielectric from negatively charged plate

Question 38

Answer 38

Question 40

Answer 40

B

Question 42

Capacitance increases for a disk making it brighter, explain why

Answer 42

Current is larger and more energy stored

Question 43

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Question 44

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Question 45

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Question 46

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Question 47

c) calculate total horizontal deflection of particle that occurs when falling between the plates

Answer 47

Question 48

Explain why time to fall vertically between the plates is independent of mass of a particle

Answer 48

Force on particle is F=mg, acceleration is equal to F/m, hence acceleration is always g Time to fall dependent on distance and acceleration

Question 49

State why two particles wity different masses and charges do not have same horizontal acceleration passing through an electric field

Answer 49

Mass is not constant, particle mass will vary Charge on particle not constant a = Eq/m Electric field strength constant but charge and mass vary so they are unlikely to be the same

Question 50

Answer 50

Question 51

Answer 51

C

Question 52

Answer 52

Potential is higher at X compared to Y Moving from high to low potential Electron is negatively charged so force it experiences us in opposite direction to the electric field Electric field is directed from X to Y so it moves towards X Since electron moves to a lower potential, it's electric potential energy increases as it moves against force acting on it A is correct answer

Question 53

Last line says increases by 4.0 x 10^-16 J

Answer 53

Question 54

Answer 54

Electric field always points from high potential to lower potential Hence correct answer is B

Question 55

Answer 55

Electrons travel in opposite direction to field lines A is correct answer

Question 56

Answer 56

Question 57

Answer 57

D is correct answer Not c because work done can also be negative so it cancels out

Question 58

Answer 58

A

Question 59

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Question 60

Answer 60

Question 61

Answer 61

C

Question 62

Answer 62

C

Question 63

Answer 63

B

Question 64

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Question 65

Answer 65

Question 66

Define an electric potential at a point in an electric field

Answer 66

Work done of a positive charge in moving charge from infinity

Question 67

Answer 67

Question 68

Answer 68

Ome is radial field and the other is uniform

Question 69

Answer 69

Question 70

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Question 71

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Question 72

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Question 73

If the potential difference between a pair of identical, parallel, conducting plates is known, what is the only additional knowledge required to determine the electric field strength between the plates? A the permittivity of the medium between the plates B the separation and area of the plates C the separation and area of the plates and the permittivity of the medium between the plates D the separation of the plates

Answer 73

D

Question 74

What is the effect of force acting on any particle in terms of motion

Answer 74

causes particle to speed up or accelerate

Question 75

An electron is travelling to the right until it enters a uniform vertical field going downards, state the direction electron travels in

Answer 75

still travels to the right but starts going upwards, remember electron has negative charge so goes in opposite direction to field

Question 76

A charged particle is held in equilibrium by the force resulting from a vertical electric field. If the electric field acts upwards, state the sign of the charge carried by the particle

Answer 76

The particle is in equilibrium, meaning the upward force due to the electric field is balancing the downward gravitational force. Since the electric field is acting upwards and the particle is in equilibrium (with gravity pulling it down), the electric force must counteract gravity. Therefore charge must be positive

Question 77

Define the electric potential at a point in an electric field.

Answer 77

work done per unit charge on a small positive test charge in moving charge from infinity to that point in the field

Question 78

Define the capacitance of a capacitor

Answer 78

charge stored per unit potential difference

Question 79

Explain why the rate of discharge will be greater if the fixed resistor has a smaller resistance. Assume potential difference is constant

Answer 79

current is larger for given V because resistance is lower current is rate of flow of charge larger flow of charge implies a greater rate of dishcarge

Question 80

lets say you have two charges and they both have field lines to represent them. How do you tell which charge has a greater magnitude

Answer 80

- amount of lines - spacing between field lines

Question 81

Give reasons why a capacitor is not a suitable source for powering a cordless telephone

Answer 81

- capacitor would be impossibly too large to fit in phone - capacitor would need charging very frequently / could only power phone for a short time - capacitor voltage [or current supplied or charge] would fall continuously whilst in use

Question 82

State and explain what, if anything, will happen to the magnitude of the electrostatic force acting on an electron as it starts to move in a uniform electric field

Answer 82

electrostatic force is unchanged as electric field strength is constant

Question 83

a proton and an electron are both placed in a radial field a) how do their electrostatic forces compare b) how magnitude of initial acceleration compares c) what happens to acceleration as they move in this electric field

Answer 83

a) they both have same charges so they have same forces b) mass of proton is much larger than that of an electron hence its acceleration is much smaller c) acceleration of proton increases as it move in the radial field where the field lines are closer together, acceleration of electron decreases due its charge being negative and moving the other way

Question 84

Answer 84