electricity

Question 1

electric current

Answer 1

rate of flow of charge

Question 2

potential difference

Answer 2

energy transferred per unit charge

Question 3

ohm’s law

Answer 3

current is directly proportional to potential difference, providing the temperature and other physical conditions remain the same

Question 4

ohmic conductor

Answer 4

a conductor where I is directly proportional to V

Question 5

non-ohmic conductor

Answer 5

a conductor where I is not directly proportional to V

Question 6

resistance of a voltmeter and ammeter

Answer 6

voltmeter resistance is infinite
ammeter resistance is zero

Question 7

ρ, R, A and L in resistivity equation

Answer 7

ρ is resistivity; R is resistance; L is length and A is the cross-sectional area

Question 8

resistivity

Answer 8

ρ = RA/L

Question 9

in metals, resitivity is proportional to

Answer 9

temperature as conducting electrons lose more energy in collisions with positive ions at a greater temperature due to greater vibrations

Question 10

units of resistivity

Answer 10

Ω m

Question 11

superconductor

Answer 11

a material with zero resistivity when cooled to or below critical temperature

Question 12

use of superconductors

Answer 12

can carry large currents with no energy losses and produce strong magnetic fields
MRI scanners
Maglev trains (magnetic levitation)
Particle accelerators eg Large Hadron Collider

Question 13

critical temperature

Answer 13

temperature at and below which a material has zero resistivity or resistance

Question 14

emf

Answer 14

actual energy provided by the battery/cell per unit charge OR the terminal potential difference across the battery when no current is flowing

Question 15

internal resistance

Answer 15

the hindrance to the flow of charge in the battery OR the loss of potential difference per unit current

Question 16

‘Lost’ potential difference

Answer 16

potential difference dropped across the internal resistance of a cell

Question 17

what is a potential divider

Answer 17

a combination of resistors in series connected across a voltage source designed to share the potential difference in a given ratio. it can be used with power source of fixed emf to provide variable power output

Question 18

how resistance of an NTC thermistor and wire change with increasing temperature

Answer 18

NTC Thermistor : resistance decreases as temperature increases
Wire : resistance increases as temperature increases

Question 19

How resistance of an LDR changes with increasing light intensity

Answer 19

resistance decreases with increasing light intensity

Question 20

potential difference across a diode in forward bias

Answer 20

a potential difference of 0.6V is dropped across a diode in forward bias

Question 21

potential difference across cells in series and parallel

Answer 21

in series, potential difference of each cell adds up
in parallel, potential difference is the same as each cell’s potential difference

Question 22

how to find emf and internal resistance from graph of pd against current

Answer 22

emf is y-intercept
internal resistance = -gradient

Question 23

resistance in series and parallel

Answer 23

series: R(total) = R(1) + R(2) + …
parallel: 1/R(total) = 1/R(1) +1/R(2) + …

Question 24

power

Answer 24

rate at which energy is transferred
P=IV, P=V^2 /R, P=I^2 *R

Question 25

charge and energy conservation

Answer 25

charge and energy are both conserved in d.c. circuits hence emf = I(R+r)

Question 26

Kerchoff’s 1st law

Answer 26

total current entering a junction = total current leaving a junction