Electricity

Question 1

Current

Answer 1

Rate of flow of charge

Question 2

Voltage

Answer 2

Work done per unit charge

Question 3

Electromotive Force

Answer 3

Work done by a voltage source per unit charge

Question 4

Resistivity Experiment

Answer 4

1.Measure diameter of test wire in several places using micrometer and calculate a mean CSA
2.Set up circuit
3.Attach crocodile clip to the test wire and measure the length between junction and crocodile clip
4.Record current and voltage
5.Calculate resistance
6.Repeat steps 3-5 with different wire lengths
7.Plot graph x-length y-resistance
8.Calculate gradient
9.Multiplay gradient by CSA to get resistivity

Question 5

Ohm’s Law

Answer 5

The current through an Ohmic conductor is directly proportional to the PD across it at a constant temperature

Question 6

How does the resistance of:
Conductors
Thermistors (negative temperature coefficient)
LDRs
vary with current,temperature and light intensity.

Answer 6

Conductor- Resistance increases as temperature increases
Thermistor- Resistance decreases as temperature increases
LDRs- Resistance decreases as light intensity increases

Question 7

Superconductivity and uses

Answer 7

Superconductors have zero resistivity/resistance below their critical temperatures
Uses:
Power transmission (no heat loss in superconducting cables)
Making string magnets (magnetically levitated trains)

Question 8

Draw IV graph for:
Ohmic conductor
Filament bulb
Thermistor
Diodes (LED)

Answer 8

check

Question 9

Kirchoff’s 1st law

Answer 9

Conservation of charge
Total current entering junction= total current leaving junction
I¹=I²+I³

Question 10

Kirchoff’s 2nd Law

Answer 10

Conservation of Energy
Total emf around a loop= total potential difference dropped across components in loop

Question 11

Series circuits

Answer 11

Resistance RT= R¹+R²+R³
Current SAME for all components
Voltage DIVIDED between components in direct proportion to their resistances

Question 12

Parallel circuits

Answer 12

Resistance 1/RT=1/R¹+1/R²+1/R³
Current uses Kirch1st I¹=I²+I³
Voltage SAME across all components

Question 13

Potential Divider and uses

Answer 13

A group of resistors connected in series across a voltage source that splits voltage between the resistors in direct proportion to their resistances to supply the desired potential difference to a component

Question 14

Internal Resistance

Answer 14

The resistance of the materials within the battery/cell

Question 15

Terminal Potential Difference

Answer 15

The potential difference measured across the terminals of a power source

Question 16

Measuring Internal Resistance

Answer 16

1.Set up the circuit
2.Vary resistance if the variable resistor
3.Record values of current and voltage for each value of R
4.Plot V against I
5.Rearrange ³=V+Ir V=-rI+³
6.The negative of the gradient is the internal resistance of the cell r
7.The y-intercept is the emf of the cell ³