Energy, power, resistance 4.2

Question 1

potential difference

Answer 1

the work done per unit of charge. the difference between two points in circuit
in volts

Question 2

what does the curly e represent in electricity

Answer 2

electromotive force (emf)

Question 3

difference between voltage and emf

Answer 3

Voltage is energy transferred per coulomb across a load resistance
Emf is the total amount of work done by the battery per coulomb

Question 4

give equation relating energy transferred to voltage

Answer 4

W=VQ

Question 5

resistance

Answer 5

how difficult it is for current to flow through an appliance
potential difference required for each unit of current that flows through a resistor

Question 6

definition of 1 Ohm

Answer 6

when a resistor is subject to a volatge of 1V and allows a curreent of 1A through, its resistance is 1 Ohm

Question 7

what is meant by ohmic conductor

Answer 7

conductor that obeysd Ohm’s law

Question 8

what does Ohm’s law say

Answer 8

the current through an ohmic conductor is directly proportional to the potential difference across it
only true if temperature is constant

Question 9

what graph represents ohmic conductor

Answer 9

line has constant gradient and passes through origin
shows that voltage is directly proportional to current

Question 10

why is filament lamp graph curved

Answer 10

the flow of current causes collisions between the electrons and metal lattice
collisions increase the temperature of lattice
as temperature increases, more collisions occur, causing resistance to increase

Question 11

what is a diode

Answer 11

an appliance that only allows current to flow in one direction

Question 12

what is a LDR

Answer 12

a semiconductor that is sensitive to light; as the light intensity increases the resistance decreases

Question 13

how does a thermistor work

Answer 13

as temeprature increases, resistance decreases
negative temperature coefficient

Question 14

what is resistivity

Answer 14

resisitivuty is a property of a metal which shows how easy/difficult it is for current to flow in material at specific temp

Question 15

how is resistivity of metals and semiconductors different with temperature

Answer 15

resistivity in metals increases with temperature because metal ions heat up vibrate more and electrons clash into them and slow down
some semiconductors get less resistive as temp increases because supplying energy actually causes more charge carriers to be released, so current can flow more easily

Question 16

power

Answer 16

the rate of energy transfer

Question 17

why do electricty companies use units in kWh rather than joules/watts

Answer 17

joules and watts are both so small that it would be tens/hundreds/millions each month - impractical to have such large numbers used.