4.2 energy, power and resistance

Question 1

ammeter

Answer 1

Question 2

voltmeter

Answer 2

Question 3

cell

Answer 3

Question 4

light bulb

Answer 4

Question 5

diode

Answer 5

Question 6

light-emitting diode (LED)

Answer 6

Question 7

resistor

Answer 7

Question 8

variable resistor

Answer 8

Question 9

thermistor

Answer 9

Question 10

light-dependant resistor

Answer 10

Question 11

heater

Answer 11

Question 12

electric motor

Answer 12

Question 13

e.m.f definition

Answer 13

work done per unit charge, transferring energy to electrical energy.

Question 14

e.m.f equation

Answer 14

W is the energy transferred

Question 15

p.d definition

Answer 15

work done per unit charge transferring energy from electrical energy into other energy stores

Question 16

p.d equation

Answer 16

W is energy transferred

Question 17

unit for p.d

Answer 17

Volt = 1 J C-1

Question 18

how must voltmeters be connected in a a circuit

Answer 18

in series

Question 19

resistance definition

Answer 19

measure of the difficulty of making current pass through it

Question 20

resistance equation + unit

Answer 20

unit = Ω

Question 21

ohm’s law states:

Answer 21

the current through a conductor is directly proportional to the potential difference across it

Question 22

resistivity of a material definition

Answer 22

the resistance of a 1m length of the material that has a cross-sectional area of 1m2

Question 23

resistivity equation + unit:

Answer 23

Ωm

Question 24

what can resistivity depend on?

Answer 24

temperature and light intensity

Question 25

what does a positive temperature coefficient mean?

Answer 25

resistance increases with temperature

Question 26

why does resistance increase with temperature in a metal

Answer 26

• at higher temps, the atoms and ions vibrate more, increasing the chance of collisions
• slows the charge carriers down, so there is a lower current per volt
• R = V/I so R increases

Question 27

what happens to the resistance of a negative temperature coefficient thermistor as temperature increases

Answer 27

decreases

Question 28

why does the R of a NTC decreases as T increases

Answer 28

• because its made from a semiconductor
• n in a semiconductor increases with T
• higher current/p.d
• R = V/I so R decreases

Question 29

resistance of an LDR as light intensity increases

Answer 29

decreases

Question 30

current voltage graph axis

Answer 30

V on x-axis
I on y-axis

Question 31

I-V graph for an ohmic conductor

Answer 31

• current proportional to p.d
• straight line through origin
• R = 1/grad

Question 32

I-V graph for a filament lamp

Answer 32

• gradient decreases because R of lamp increases
• R = V/I at any point

Question 33

I-V graph for diode or LED

Answer 33

• shows diode only lets current flow in one direction
• shows p.d must be above threshold before any current can flow
• R = V/I at any point

Question 34

I-V graph for a NTC

Answer 34

• shows resistance decreases as gradient increases
• R=V/I at any point

Question 35

power equations + unit

Answer 35

• P = IV
• P = I2R
• P = V2/R
• watt

Question 36

energy transferred

Answer 36

W = IVt

Question 37

energy unit

Answer 37

J or kWh

Question 38

how to calculate energy in kWh and J

Answer 38

energy (kWh) = power (kW) x time (h)
1kWh = 1000W x 60 x 60 = 3.6MJ

Question 39

how to calculate cost of electricity

Answer 39

multiplying energy in kWh by the cost of 1kWh in pence

Question 40

what happens to the charged particles between two points of p.d

Answer 40

the p.d will accelerate the particles

Question 41

energy transferred to a charged particle equation:

Answer 41

E = eV
e is charge
V is difference in p.d