Paper 1, Topic 3 - Electric Circuits

Question 1

What is the definition of current?

Answer 1

The rate of flow of charge in a circuit.

Question 2

What is the definition of current as an equation?

Answer 2

Current = ΔQ / Δt

Question 3

What is the definition of potential difference?

Answer 3

The work done per coulomb of charge travelling in a circuit.

Question 4

What is the definition of voltage as an equation?

Answer 4

Voltage = W / Q

Question 5

What is the ideal resistance for a voltmeter and why?

Answer 5

The ideal voltmeter should have an infinite resistance so that no current is drawn from the circuit.

Question 6

What is an ohmic conductor?

Answer 6

The current flowing through the conductor is directly proportional to potential difference, when held at a constant temperature.

Question 7

What is resistivity?

Answer 7

A measure of how easily it allows charge to flow through it.

Question 8

What is the equation for resistivity?

Answer 8

⍴ = RA / L

Question 9

Which eqaution is used to work out the current through a wire?

Answer 9

I = nqvA

Question 10

What is a superconductor?

Answer 10

A materials which have zero resistivity at and below a critical temperature.

Question 11

What is a semiconductor?

Answer 11

Components for which the resistance changes depending on external conditions.

Question 12

How does light intensity affect the resistance of an LDR?

Answer 12

When light intensity increases, resistance decreases. This is because electrons are released so there are more charge carriers.

Question 13

How does resistance vary with temperature in an NTC thermistor?

Answer 13

When temperature increases, resistance decreases.

Question 14

How does resistance vary with temperature in a PTC thermistor?

Answer 14

When temperature increases, resistance increases.

Question 15

What are three equations for power?

Answer 15

P = I x V
P = I² x R
P = V² / R

Question 16

What happens to the current in a filament lamp as voltage is increased?

Answer 16

As the voltage increases, so does the current.
This increases the temperature of the filament.
This causes the metal ions to vibrate therefore making it harder for charge carriers to pass through as there are more collisions.
This means the resistance increases.

Question 17

What is the function of a diode?

Answer 17

Diodes only let current flow through it in one direction.

Question 18

What is the threshold voltage of a diode?

Answer 18

0.6 V

Question 19

In which series is current the same in all positions of the circuit?

Answer 19

Series

Question 20

In which series is voltage split between all the components?

Answer 20

Series. The voltage is split in the ratio of their resistances.

Question 21

In which circuit is the potential difference the same?

Answer 21

Parallel. The voltage is the same across each loop but is then split between all components on that loop.

Question 22

In which circuit is current split ?

Answer 22

Parallel

Question 23

What is Kirchhoff’s first law?

Answer 23

The total current entering a junctions is equal to the total current leaving it.

Question 24

What is Kirchhoff’s second law?

Answer 24

The sum of e.m.f in any loop of the circuit is equal to the sum of the p.d’s of each component.

Question 25

What does EMF stand for?

Answer 25

Electromotive force.

Question 26

What is the definition of EMF?

Answer 26

The amount of energy supplied by the source per unit charge.

Question 27

Why is terminal potential difference of the power source never equal to the EMF value?

Answer 27

Energy is dissipated within the source due to the cell’s internal resistance.

Question 28

What are two equations for calculating EMF?

Answer 28

ε = I x R + I x r
ε = V + r x I

Question 29

When plotting a graph of terminal voltage against current, what does the y intercept show?

Answer 29

The EMF.

Question 30

When plotting a graph of terminal voltage against current, what does the gradient show?

Answer 30

The negative internal resistance.