5.1 Current electricity

Question 1

Define electric current.

Answer 1

Rate of flow of charge

Question 2

Define potential difference.

Answer 2

Work done moving a unit charge between two points.

or work done per unit charge

Question 3

Define resistance.

Answer 3

A measure of how difficult it is for current to flow.

Question 4

State Ohm’s law.

Answer 4

For an Ohmic conductor, current is directly proportional to the potential difference across it.

Question 5

What does does an IV graph for an Ohmic conductor look like?

Answer 5

Question 6

What does does an IV graph for a semiconducting diode look like?

Answer 6

Question 7

What does does an IV graph for a filament bulb look like?

Answer 7

Question 8

How can you measure current?

Answer 8

With an ammeter connected in series.

Question 9

How can you measure potential difference?

Answer 9

With a voltmeter connected in parallel

Question 10

What is special about an ideal ammeter?

Answer 10

An ideal ammeter has zero resistance.

Question 11

What is special about an ideal voltmeter?

Answer 11

An ideal voltmeter has infinite resistance.

Question 12

Define resistivity.

Answer 12

The resistance of a 1m cylinder with CSA of 1m²

Question 13

What effect does temperature have on the resistance of a metal conductor?

Answer 13

Increase in temperature will increase the vibrations of the ion lattice, increasing resistance.

Question 14

What effect does temperature have on the resistance of a thermistor?

Answer 14

Increase in temperature will release more electrons from atomic bonds, descreasing resistance.

Question 15

What is meant by ‘negative temperature coefficient?’

Answer 15

Increase in temperature decreases resistance.

These are the only type of thermistor you’ll see

Question 16

Describe a resistance-temperature grapgh of a thermistor.

Answer 16

Question 17

What effect does light have on the resistance of a light dependent resistor (LDR)?

Answer 17

Increase in light intentisty will release more electrons from atomic bonds, descreasing resistance.

Question 18

What is a superconductor?

Answer 18

A material with zero resistivity below a critical temperature.

Critical temperature is an inherent material property

Question 19

What is the graph of resistivity vs temperature for a superconductor?

Answer 19

Question 20

How do you add resistors in series?

Answer 20

R_{total</sup>=R1</sup>+R2</sup>+R3</sup>+…}

Question 21

How do you add resistors in parallel?

Answer 21

Question 22

What is the energy transferred to a component in time t?

Answer 22

E=IVt

Question 23

Define power.

Answer 23

Rate of energy transfer.

Question 24

What are the 3 equations for power in an electrical circuit?

Answer 24

Question 25

What is the power rating of a resistor?

Answer 25

Maximum power a resistor can withstand.

Question 26

What can be said about the current in a series circuit?

Answer 26

Current is the same everywhere in the circuit.

Question 27

What can be said about the voltages in a series circuit?

Answer 27

The sum of voltages across all components is equal to the supply p.d.

Question 28

What can be said about the current in a parallel circuit?

Answer 28

The sum of currents across all parallel set of branches is equal to the total current.

Question 29

What can be said about the voltages in a parallel circuit?

Answer 29

The potential difference across each branch is the same.

Question 30

What happens when multiple cells are connected in series?

Answer 30

The total voltage across the cells is equal to the sum of the indiviual voltages of the cells. | V_{total=V1+V2+V3+...}

Question 31

What happens when multiple **identical** cells are connected in parallel?

Answer 31

The total voltage is equal to the voltage of one cell. | V_{total=V1=V2=V3=...}

Question 32

What is Kirchoff's first law?

Answer 32

Total current flowing into a junction is equal to the current flowing out of that junction. | Shows no charge is lost at any point in a circuit (charge conservation)

Question 33

What is Kirchoff's second law?

Answer 33

Sum of all volatges in a series circuit is equal to the supply voltage. | Shows no energy is lost at any point in a circuit (energy conservation)

Question 34

What is a potential divider?

Answer 34

A circuit with at least two resistors in series connected across a voltage source.

Question 35

How does a potential divider work?

Answer 35

The potential difference being split into a ratio across the series resistors

Question 36

What is the potential divider equation?

Answer 36

Question 37

What 2 purposes are a potential dividers used for?

Answer 37

To provide a constant potential difference or to provide a variable potential difference.

Question 38

Define emf.

Answer 38

Work done in moving 1 C of charge whole way round the circuit.

Question 39

Define internal resistance.

Answer 39

Resistance inside the cell. | Electrons collide aith atoms inside cell

Question 40

Define lost volts.

Answer 40

Voltage lost due to internal resistance. | Energy wasted from electrons colliding with atoms in cell.

Question 41

Define terminal potential difference.

Answer 41

Is the emf minus the p.d. on the internal resistance.

Question 42

What is the equation for emf involving internal resistance?

Answer 42