Module 4.2 - Electricity: Energy, Power and Resistance

Question 1

What is potential difference?

Answer 1

The energy transferred per unit charge across a COMPONENT

Question 2

What are the units of potential difference?

Answer 2

Volts or J/C

Question 3

Define electromotive force

Answer 3

Energy gained per unit charge by charges passing through SUPPLY

Question 4

What is the difference between e.m.f. and p.d.?

Answer 4

e.m.f. is the energy transferred to each unit charge from a SUPPLY, p.d. is the energy transferred by each unit charge to a COMPONENT.

Question 5

How do you work out the energy transferred to each unit charge from a supply using the e.m.f?

Answer 5

Work done = em.f. x charge

Question 6

How do you work out the energy transferred by each unit charge to a component using p.d.?

Answer 6

Work done = p.d. x charge

W = VQ

Question 7

How is the energy transferred to each charged particle, eV, calculated?

Answer 7

eV = 1/2mv^2

e - charge of electron
V - p.d.
m - mass of electron
v - velocity of electron

Question 8

What is Ohm’s law?

Answer 8

Current through a conductor is DIRECTLY PROPORTIONAL to the potential difference across it

Question 9

What is Ohm’s law in equation form?

Answer 9

V = IR

Question 10

What is the unit of resistance?

Answer 10

Ohm - Ω

Question 11

What are the 4 factors that affect resistance?

Answer 11

> Material
Length of wire
Cross-sectional area
Temperature

Question 12

How does the material affect resistance ?

Answer 12

Different electrical properties

Question 13

How does the length of wire affect resistance?

Answer 13

As length increases, resistance increases - therefore current decreases.

Question 14

How does the cross-sectional area of the wire affect resistance?

Answer 14

As area increases, resistance decreases - current increases

Question 15

How does temperature affect resistance?

Answer 15

As temperature increases, resistance increases

Question 16

What are ohmic conductors?

Answer 16

Conductors that obey Ohm’s law

Question 17

What type of property is resistivity and what is not affected by?

Answer 17

An intrinsic property that is not affected by physical dimension

Question 18

How do you work out the resistance of a material using its resistivity?

Answer 18

R = (p x L) ÷ A

Question 19

What is resistivity affected by?

Answer 19

Temperature

Question 20

How are the resistivity of metals affected by temperature?

Answer 20

As temperature increases, resistivity increases

Question 21

How are the resistivity of some semiconductors affected by temperature?

Answer 21

As temperature increases, the resistivity decreases

Question 22

What is an NTC thermistor?

Answer 22

Negative temperature coefficient thermistor - as temperature increases, resistance decreases

Question 23

What is a PTC thermistor?

Answer 23

Positive temperature coefficient - as temperature increases, resistance decreases

Question 24

How do you work out power using current and voltage?

Answer 24

P = VI

Question 25

How do you work out power using current and resistance?

Answer 25

P = I^2 x R

Question 26

How do you work out power using voltage and resistance?

Answer 26

P = V^2 ÷ R

Question 27

How do you work out the electrical work done using charge and voltage?

Answer 27

W = QV

Question 28

How do you work out electrical work done using current, voltage and time?

Answer 28

W = V x I x t

Question 29

What is a kW h?

Answer 29

> Unit of energy

> 1000 watts for 3600 secs = 3,600,000J

Question 30

How you convert from J to kW h?

Answer 30

÷ 3,600,000

Question 31

How do you convert from kW h to J?

Answer 31

x 3,600,000