Electricity

Question 1

Define electric current

Answer 1

rate of flow of charge

Question 2

What does electric current of one amp represent?

Answer 2

rate of flow of charge of one coulomb per second

Question 3

Name the instrument used to measure current

Answer 3

ammeter

Question 4

Define potential difference

Answer 4

V = W/ Q

Question 5

Name the instrument used to measure the p.d between two points in a circuit

Answer 5

voltmeter

Question 6

What is the resistance of a component and how is it defined?

Answer 6

measure of how much a component opposes the flow of current

R = V/I

Question 7

State Ohm’s law

Answer 7

current through a metallic conductor is directly proportional to the p.d across it, provided physical conditions do not change

Question 8

What is the name for a conductor that obeys Ohm’s law?

Answer 8

ohmic conductor, constant resistance

Question 9

What is the I-V characteristic of a component?

Answer 9

graph which shows how the current through the component varies with the p.d across it

Question 10

Describe the I-V characteristic for an ohmic conductor

Answer 10

straight line graph through the origin

Question 11

Describe the I-V characteristic for a filament lamp

Answer 11

curve with decreasing gradient

Question 12

Describe the i-v characteristic of a diode

Answer 12

with forward bias, graph starts at 0,0 and increases gradually, with reverse bias hrap extends along the negative p.d with almost 0 current

Question 13

What is a negative temperature coefficient thermistor?

Answer 13

Component for which resistance decreases with higher temperatures

Question 14

What is a superconductor?

Answer 14

material with zero resistivity at and below a certain temperature

Question 15

Why are superconductors useful?

Answer 15

Current has no heating effect so no energy lost

Question 16

State the law of conservation of charge

Answer 16

charge cannot be created or destroyed, so the amount of charge in a closed system remains the same

Question 17

State Kirchhoff’s first law

Answer 17

Total current leaving a junction = total current entering junction

Question 18

Define the potential difference between two points in a circuit

Answer 18

energy transferred per coulomb of charge that flows from one point to the other

Question 19

What is potential drop in a circuit?

Answer 19

p.d between two points in a circuit if the charge carriers lose energy

Question 20

State Kirchhoff’s Second law

Answer 20

sum of the emfs around any loop in a circuit = sum of p.ds around the loop

Question 21

Give the potential difference rule for two or more components in series

Answer 21

total p.d across all the components = sum of the potential differences across each component

Question 22

What can a potential divider circuit do as part of a sensor circuit?

Answer 22

supply a p.d that varies with physical conditions

Question 23

What is a potentiometer?

Answer 23

variable potential divider that uses a single variable resistor to allow Vout to be varied from 0V to the maximum source p.d

Question 24

Define the electromotive force of a power supply and give its unit

Answer 24

electrical energy per unit charge produced by the power source, volts

Question 25

Give the equation relating to emf of a power supply to its internal resistance, the current in the circuit, and the external resistance

Answer 25

emf = I(R+r)

Question 26

Give the equation for calculating lost p.d across a power supply’s internal resistance

Answer 26

lost p.d = Ir

Question 27

What is the benefit of connecting cells in parallel?

Answer 27

providing longer-lasting energy supply because the total energy store is greater