Topic 3

Question 1

Define electrical current

Answer 1

Electrical current is the rate of flow of charge

Question 2

State the defining equation for current

Answer 2

I = ΔQ / Δt

Question 3

What is the unit of current

Answer 3

Ampere (Amps), A

Question 4

Define voltage

Answer 4

Voltage is the work done per unit charge

Question 5

State the defining equation for voltage

Answer 5

V = W / Q

Question 6

What equation links current, voltage and resistance?

Answer 6

Voltage (V) = Current (A) x Resistance (Ω)

V=IR

Question 7

What is ohm’s law?

Answer 7

If Ohm’s law is obeyed, the current and voltage passing through a component are directly proportional, when at a constant temperature

Question 8

Describe the distribution of current in a series circuit

Answer 8

In a series circuit, the current is the same at all positions in the circuit

Question 9

What law is the distribution of current in a series circuit a consequence of?

Answer 9

The law of the conservation of charge. Charge cannot be created or destroyed and so in a closed loop, the flow of charge must be the same throughout

Question 10

Describe the distribution of current in a parallel circuit

Answer 10

In a parallel circuit, the current is split between the different branches. The current entering each branch must be the same as the current leaving it

Question 11

Explain how the conservation of charges applies to parallel cicuits

Answer 11

Charge cannot be created or destroyed meaning the total current leaving the source must equal the sum of the currents in all the individual branches

Question 12

What law is the distribution of potential differences in a circuit a consequence of?

Answer 12

The law of the conservation of energy

Question 13

Describe the distribution of potential differences in a series circuit

Answer 13

The total potential difference is split across all the components in a series circuit, in the ratio of their resistances.

Question 14

Describe the distribution of potential differences in a parallel cicuit

Answer 14

The sum of the potential differences in each branch of a parallel circuit, is the same and will be equal to the potential difference of the source

Question 15

What equation relates power, current and potential difference?

Answer 15

P=IV

Question 16

How can you calculate the work done over a given time period, by a component with a known potential difference and current?

Answer 16

Combining P = W/t and P=IV gives:

W=IVt

Question 17

What is the IV characteristic for an ohmic conductor?

Answer 17

Directly proportional

Question 18

Explain the IV characteristic for a filament bulb

Answer 18

The higher the current, the higher the temperature of the metal filament
The higher the temperature, the higher the KE of the metal ions and so the more they vibrate
This makes it harder for current to flow and so the resistance of the bulb increases

Question 19

What three physical factors affect the resistance of a wire?

Answer 19

Length
Cross-Sectional Area
Resistivity

Question 20

How does increasing the length of a conductor affect its resistance?

Answer 20

The longer the conductor is, the higher its resistance, assuming all other factors remain the same

Question 21

How does increasing the cross-sectional area of a conductor affect its resistance?

Answer 21

The larger the cross-sectional area of a conductor, the lower its resistance, assuming all other factors remain the same

Question 22

What is resistivity?

Answer 22

A characteristic property of a material that determines its resistance to current flow

Question 23

Compare the resistance of two conductors of the same dimensions, but with different resistivities

Answer 23

The conductor with the higher resistivity will have the higher resistance

Question 24

State the equation linking the factors affecting the resistance of a conductor

Answer 24

R = ρL / A

Question 25

What equation links the number of charge carriers in a metal, along with their drift velocity, to the current flow?

Answer 25

I = nqAv

Question 26

How does the potential along a uniform current-carrying wire vary as you move along it?

Answer 26

The potential will increase as you move along the wire

Question 27

What is the electromotive force of a power supply?

Answer 27

The electromotive force is the amount of energy that is transferred to each Coulomb of charge that passes through it

Question 28

What is the terminal potential difference of a power supply?

Answer 28

The terminal potential difference of a power supply is the actual potential difference that is produced across the terminals of the supply and is provided to the circuit

Question 29

Why does the electromotive force of a supply differ from its terminal potential difference?

Answer 29

Some of the energy that is transferred to the charges is used to overcome the internal resistance of the power supply

Question 30

Define internal resistance

Answer 30

The internal resistance of a power supply is the electrical resistance, when a current flows, due to the materials within the supply itself

Question 31

Describe a method to determine the terminal potential difference of a battery

Answer 31

Attach a voltmeter directly across the terminals of the battery when it is isolated. Since no current flows, no potential is lost due to internal resistance and so the voltmeter will read the value of the terminal p.d.

Question 32

What is a semiconductor?

Answer 32

A semiconductor is a component that can change its resistance based on external conditions

Question 33

Give two examples of semiconductors and state what they are sensitive to

Answer 33

Thermistors are sensitive to temperature | LDRS are sensitive to light

Question 34

Describe how the resistance of a thermistor changes as temperature decreases

Answer 34

As temperature decreases, the resistance of a thermistor will increase

Question 35

Explain why the resistance of a thermistor will decrease with an increase of temperature

Answer 35

As temperature increases, conduction electrons are liberated, meaning there are more charge carriers and so current can flow more easily

Question 36

Describe how the resistance of an LDR changes as light intensity increases

Answer 36

As light intensity increases, the resistance of an LDR will decrease

Question 37

What is a potential divider?

Answer 37

A potential divider is a pair of resistors used to split the potential difference over them into a given ratio

Question 38

What is the link between the resistances and the potential differences in a potential divider?

Answer 38

The potential difference of the circuit is split in the ratio of the resistances of the resistors