Electricity 1

Question 1

Define current

Answer 1

the rate of flow of charge

Question 2

Which way does conventional current flow?

Answer 2

positive to negative

Question 3

How should an ammeter be connected?

Answer 3

in series

Question 4

What is one coulomb?

Answer 4

the charge that flows past a point in one second when there is a current of one amp

Question 5

What is Kirchhoff’s first law?

Answer 5

the total current that enters a junction is equal to the total current that leaves a junction

Question 6

Define potential difference

Answer 6

the work done when one coulomb of charge moves between two points

Question 7

Define electromotive force (EMF)

Answer 7

the amount of electrical energy a power supply transfers to each coulomb of charge

Question 8

What is the relationship between current at each point in a series circuit?

Answer 8

current is the same at all points

Question 9

What is Kirchhoff’s second law?

Answer 9

the total EMF around a series circuit is equal to the sum of the potential difference across each component

Question 10

How should a voltmeter be connected?

Answer 10

in parallel

Question 11

Define power

Answer 11

the rate of doing work

Question 12

Define resistance

Answer 12

the rate of potential difference across a component to the current through the component

Question 13

What is ohm’s law?

Answer 13

for an ohmic conductor at a constant temperature, the current is directly proportional to the potential difference across it

Question 14

What is the I-V graph for an ohmic conductor?

Answer 14

directly proportional graph

Question 15

What is the I-V graph for a diode?

Answer 15

I is very small (basically zero) up to the threshold voltage of 0.6V where I increases almost vertically

Question 16

Give an example of an ohmic conductor

Answer 16

a resistor

Question 17

What is the threshold frequency for a diode?

Answer 17

0.6V

Question 18

What is the I-V graph for a filament lamp

Answer 18

• I and V are initially directly proportional

- After, for the same increase in V, the increase in I becomes progressively smaller

Question 19

Explain the I-V graph of a filament lamp

Answer 19

1) as voltage increases, current increases
2) As current increases, temperature increases and thus positive ions vibrate more
3) Therefore electrons collide with positive ions more frequently
4) Therefore resistance increases

Question 20

How much resistance can ammeter be assumed to have?

Answer 20

0 resistance

Question 21

How much resistance can voltmeters be assumed to have?

Answer 21

infinite resistance

Question 22

What happens to the resistance of a thermistor as its temperature increase?

Answer 22

As temperature increases, resistance decreases

Question 23

Why is it that as the temperature of a thermistor increases, its resistance decreases?

Answer 23

1) increasing the temperature of the thermistor causes electrons to be emitted from atoms
2) thus the number of charge carriers increases and so the current increases
3) causing resistance to decrease