Electricity

Question 1

Electric current

Answer 1

Rate of flow of charge

Question 2

The elementary charge

Answer 2

e = 1.6 x 10^-19 C

Question 3

The net charge on a particle or an object is

Answer 3

Quantised and a multiple of e

Question 4

Current

Answer 4

The movement of electrons in metal and movement of ions in electrolytes

Question 5

Current (I) =

Answer 5

Charge (Q) / time (t)

Question 6

Conventional current flows from

Answer 6

Positive to negative

Question 7

Kirchhoff’ a first law

Answer 7

At any junction in a circuit the sum of the currents entering is equal to the sum of currents leaving - the conservation of charge

Question 8

In series, the current

Answer 8

Is the same

Question 9

In parallel, the current

Answer 9

Splits between branches

Question 10

Mean drift velocity

Answer 10

The average displacement per unit time of charge carrier

Question 11

Mean drift velocity equation

Answer 11

I = Anev

Question 12

Typical n value for metal

Answer 12

10^28 m-3

Question 13

N

Answer 13

Number density of charge carriers

Question 14

Potential difference

Answer 14

The work done per unit charge by charge carriers as they move from one point to another in a circuit, transferring electrical energy to other forms

Question 15

EMF and P.d. Units

Answer 15

JC^-1 or V

Question 16

EMF/P.d. =

Answer 16

Work (j) / Charge (C)

Question 17

Difference between EMF and P.d

Answer 17

EMF is work done by a battery, P.d is the work done by charge carriers

Question 18

Kirchhoff second law

Answer 18

Around any loop in a circuit the sum of the EMFs is equal to the sum of the p.ds - conservation of energy

Question 19

Work done (energy transferred) =

Answer 19

V x Q

EMF x Q

Question 20

Energy transferred (eV) =

Answer 20

1/2 x mv^2

Question 21

Resistance unit

Answer 21

Ohm

Question 22

Resistance equation

Answer 22

R=V/I

Question 23

Resistance

Answer 23

The potential difference per unit current

Question 24

Ohms law

Answer 24

Potential difference is proportional to current for an ohmic conductor at constant temperature

Question 25

Resistor IV characteristics

Answer 25

I is directly proportional to V

Constant resistance

Question 26

V =

Answer 26

IR

Question 27

An ohmic conductor has

Answer 27

Constant resistance

Question 28

Bulb IV characteristics

Answer 28

Large current raises with temperature

V increases at a faster rate than I

Question 29

Resistivity equation

Answer 29

R = pL / A

Question 30

Resistivity (p) unit

Answer 30

Ohm m

Question 31

Resistivity

Answer 31

The resistance multiplied cross-sectional area divided by the leangths

Question 32

Light dependent resistor

Answer 32

Measures the variation of resistance with light intensity

Question 33

Power equations

Answer 33

P=IV

P=I^2 R

P=V^2/R

Question 34

W =

Answer 34

ItV

Question 35

1 kWh

Answer 35

The energy transferred by a power of 1 kW in a time of 1 hour (3.6Mj

Question 36

The resistivity of semiconductors ________ as temperatures increase

Answer 36

Decrease

Question 37

NTC thermistor

Answer 37

A Negative temperature coefficient

Question 38

The resistance of NTC will ________ as the temperature increases

Answer 38

Decrease