3 - Electricity

Question 1

Define current

Answer 1

Rate of flow of charge

Question 2

Define potential difference

Answer 2

Work done per unit charged

Question 3

Define emf

Answer 3

Total supply of voltage

Question 4

Define power

Answer 4

Rate of energy transfer

Question 5

Define resistance

Answer 5

Slows down flow of charge

Question 6

Define internal resistance

Answer 6

Resistance due to power supply

Question 7

Define efficiency

Answer 7

What proportion of energy is useful out of total energy

Question 8

Define charge carrier density

Answer 8

Number of free electrons within a metre cube

Question 9

Direction of conventional current

Answer 9

Positive to negative

Question 10

Direction of electron current

Answer 10

Negative to positive

Question 11

What is the charge on an electron?

Answer 11

-1.6x10^-19 C

Question 12

How many electrons are needed to produce 1C?

Answer 12

6.5x10^18

Question 13

Where does internal electrical resistance come from?

Answer 13

-In battery, chemical energy used to make electrons move
-Electrons colliding with atoms/ions in the battery

Question 14

Describe the distribution of current in a series circuit

Answer 14

Same at all positions in the circuit

Question 15

Describe the distribution of current in a parallel circuit

Answer 15

Current splits at the branches.
Current entering branch = current leaving branch

Question 16

Describe the distribution of potential difference in a series circuit

Answer 16

Split across all components in the ratio of their resistances

Question 17

Describe the distribution of potential difference in a parallel circuit

Answer 17

Same in each branch and is equal to voltage of the source

Question 18

What is Kirchhoff’s 1st law?

Answer 18

Total charge when reaching a junction is equal to total charge leaving a junction

Question 19

What is Kirchhoff’s 2nd law?

Answer 19

Potential difference is the same over all components in a closed circuit

Question 20

Equation for resistance in series

Answer 20

RT = R1 + R2

Question 21

Equation for resistance in parallel

Answer 21

1/RT = 1/R1 + 1/R2

Question 22

Why is an ammeter connected in series?

Answer 22

Very small resistance, meaning small voltage

Question 23

Why is a voltmeter connected in parallel?

Answer 23

Large resistance, meaning small current

Question 24

How can maximum power be reached?

Answer 24

When internal resistance and resistance are the same

Question 25

How can emf and total resistance in series be calculated?

Answer 25

Take a sum

Question 26

How can emf of several cells be calculated in parallel?

Answer 26

It is conserved throughout

Question 27

How to determine output voltage in potential divider circuits?

Answer 27

Ratios of resistances or equation

Question 28

What are 4 different charge carriers?

Answer 28

-Metals (electrons) -Electrolytes (positive/negative ions) -Plasma (electrons and positive ions) -Semiconductors (electrons and/or positive ‘holes’)

Question 29

Define drift velocity

Answer 29

Average velocity that electrons gain in a material, due to an electric field

Question 30

How does the cross-sectional area affect resistivity?

Answer 30

Greater area = easier the passage of electrons

Question 31

How does length affect resistivity?

Answer 31

Longer = harder to send current through

Question 32

How does resistance affect resistivity?

Answer 32

Larger resistance = higher resistivity

Question 33

Define superconductor

Answer 33

Materials with no resistivity at and below a critical temperature

Question 34

Uses for superconductors

Answer 34

- Reduce energy loss - produces strong magnetic fields

Question 35

What happens to resistance in a LDR when light intensity increases?

Answer 35

Resistance decreases

Question 36

What happens to resistance in a negative temperature coefficient thermistor when temperature increases?

Answer 36

Resistance decreases

Question 37

What happens to resistance in metallic conductors as temperature increases?

Answer 37

Resistance increases

Question 38

What is Ohm's Law?

Answer 38

Current and voltage passing through a component are directly proportional at a constant temperature

Question 39

Define the IV characteristic of a filament bulb

Answer 39

-Higher current = higher temperature -Higher temperature = higher E[k], so metal ions vibrate more -Ions harder to flow, so increases current

Question 40

Explain conservation of charge

Answer 40

Charge cannot be created or destroyed