Electricity

Question 1

coulomb

Answer 1

SI unit of charge

Question 2

current

Answer 2

The rate of flow of charge

Question 3

anode

Answer 3

positive electrode

Question 4

cathode

Answer 4

negative electrode

Question 5

power

Answer 5

rate of work done

Question 6

elementary charge

Answer 6

the magnitude of the charge of an electron

Question 7

describe what is meant by mean drift velocity

Answer 7

the average displacement of electrons along a wire per second, electrons collide with lattice, so go in diff dirrections

Question 8

Ohm’s Law

Answer 8

voltage and current are directly proportional when the temperature is constant. V=IR

Question 9

semiconductor examples

Answer 9

silicon and germanium

Question 10

semiconductors get hot because

Answer 10

electrons need to travel faster to get the same current

Question 11

I = Anev

Answer 11

current = area x number density x elementary charge x drift velocity

Question 12

cell symbol short side

Answer 12

negative terminal

Question 13

thermionic emission

Answer 13

the thermally induced flow of charge carriers from a surface or over a potential-energy barrier

Question 14

eV = 1/2mv^2

Answer 14

elementary charge x p.d = kinetic energy = work done on charge

Question 15

ohm

Answer 15

unit of resistance

Question 16

resistivity

Answer 16

A material’s opposition to the flow of charge.

Question 17

p = RA/L

Answer 17

resistivity = resistance x area / length

Question 18

Negative temperature coefficient

Answer 18

resistance of semiconductor decreases when temperature is increased

Question 19

Kirchoff’s Second Law

Answer 19

sum of e.m.f. is equal to sum of p.d.s in a closed loop

Question 20

potential difference

Answer 20

measure of energy transferred per unit charge between two points.

Question 21

conventional current

Answer 21

positive to negative. opposite to electron flow

Question 22

electron flow

Answer 22

negative to positive. opposite to conventional current.

Question 23

Kirchoff’s First Law

Answer 23

sum of currents entering junction is equal to sum of current out of junction

Question 24

quantised

Answer 24

charge on an object always multiple of e

Question 25

number density

Answer 25

number of free electrons per cubic metre

Question 26

cell symbol long side

Answer 26

positive terminal

Question 27

potential difference in relation to charges

Answer 27

work done by the charges, they lose energy through component

Question 28

electromotive force

Answer 28

work done on the charges, they gain energy through component

Question 29

Threshold voltage

Answer 29

The minimum potential difference at which a diode begins to conduct

Question 30

large current needed (car battery)

Answer 30

low internal resistance

Question 31

small current needed (school power supply)

Answer 31

high internal resistance

Question 32

what causes internal resistance?

Answer 32

wires and components in power supplies, chemicals in cells

Question 33

resistance

Answer 33

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

Question 34

lost volts

Answer 34

The difference between a source’s emf and the terminal voltage.

Question 35

terminal potential difference

Answer 35

The potential difference across the terminals of a power source. It is equal to the source’s emf minus any voltage drop over the source’s internal resistance.

Question 36

number density of copper?

Answer 36

10^29

Question 37

What is the difference between rms speed and drift velocity of electrons?

Answer 37

r.m.s. speed is random motion Drift velocity is the mean velocity (of the free electrons)

Question 38

What is conductivity?

Answer 38

1/resistivity

Question 39

What is band theory?

Answer 39

In semiconductors, increasing thermal energy gives electrons enough energy to move from valence band to conduction band

Question 40

Why would you connect a resistor in series with an LED?

Answer 40

Minimises current flow, ensuring it doesn't overheat.

Question 41

In series, if bulb fails, what happens to pd?

Answer 41

Components' pds can be ignored.

Question 42

If two resistors are connected in parallel, and one's resistance is 0, what is the total resistance?

Answer 42

0

Question 43

What is special about an open circuit?

Answer 43

Resistance = 0

Question 44

What is special about a shorted circuit?

Answer 44

Resistance = 0