09 Energy, Power, and Resistance

Question 1

capacitor

Answer 1

a component that stores charge, consisting of two plates separated by an insulator

Question 2

resistance

Answer 2

potential difference across a component divided by the current through it

Question 3

cell

Answer 3

a device that transfers chemical energy into electrical energy

Question 4

battery

Answer 4

a collection of cells that transfers chemical energy into electrical energy

Question 5

series

Answer 5

an arrangement of electrical components connected end-to-end that means the current is the same in each component

Question 6

polarity

Answer 6

the type of charge (positive or negative) or the orientation of a cell relative to a component

Question 7

potential difference

Answer 7

the energy transformed from electrical to other forms (1/2 marks) per unit charge (2/2)

Question 8

volt

Answer 8

derived SI unit of pd and emf, 1 volt = 1 joule of energy transferred per coulomb

Question 9

voltmeter

Answer 9

device used to measure potential difference - must be placed in parallel across components and ideally have an infinite resistance

Question 10

electromotive force (emf)

Answer 10

energy transformed from other forms to electrical (1/2 marks) per unit charge (2/2)

Question 11

electron gun

Answer 11

a device that uses a large accelerating potential difference to produce a narrow beam of electrons

Question 12

resistor

Answer 12

electrical component that obeys Ohm’s law, transferring electrical energy to thermal energy

Question 13

ohm

Answer 13

derived SI unit of resistance defined as resistance of a component that has a pd of 1V per unit amp

Question 14

Ohm’s law

Answer 14

current through a component is directly proportional to the pd across it providing the temperature, and other physical constants, remain constant. a graph of I against V is a straight line through the origin

Question 15

filament lamp

Answer 15

an electrical component containing a narrow filament of wire that transfers electrical energy into heat and light

Question 16

I-V characteristic

Answer 16

a description of the relationship between the electric current in a component and the pd across it, usually in graph form of I against V

Question 17

ohmic conductor

Answer 17

conductor that obeys Ohm’s law

Question 18

non-ohmic component

Answer 18

a component that does obey Ohm’s law eg filament lamp and diode

Question 19

light-emitting diodes (LEDs)

Answer 19

a type of diode that emits light when it conducts electricity

Question 20

threshold pd (or threshold voltage)

Answer 20

minimum pd at which a diode begins to conduct

Question 21

resistivity

Answer 21

property of a material equal to
(resistance of material x cross sectional area of material) / length of material

Question 22

thermistor

Answer 22

electrical component that has a resistance that decreases as the temperature increases (a negative temperature coefficient)

Question 23

negative temperature coefficient (NTC)

Answer 23

a relationship in which a variable decreases as temperature increases, eg the resistance of NTC thermistors

Question 24

light-dependent resistor (LDR)

Answer 24

electrical component with a resistance that decreases as the light intensity incident on it increases

Question 25

electricity meter

Answer 25

a device that measures the electrical energy supplied in kWh to a house from the grid

Question 26

kilowatt-hour (kWh)

Answer 26

unit of energy equal to 3.6MJ

Question 27

how does an electron gun produce a beam of high-speed electrons? (4 marks)

Answer 27

• electrons emitted from a hot filament at the rear of the gun
• large pd between the filament and an anode
• electrons accelerate towards the anode and pass through a gap in the anode

Question 28

effect of temperature increase on semiconductor electrical properties

Answer 28

resistivity falls, conductivity rises