Electricity

Question 1

current, charge

Answer 1

I = Q/t

Question 2

voltage, energy

Answer 2

V = E/Q

Question 3

advantage of potential divider for IV circuits instead of variable resistor

Answer 3

can make current go to zero

Question 4

ohms law

Answer 4

I ∝ V
provided physical conditions constant

Question 5

IV graph for ohmic things such as resistor or wire

Answer 5

linear graph
resistance = 1/gradient

Question 6

IV graph axis

Answer 6

I on y axis
V of x axis

Question 7

Bulb IV graph

Answer 7

temp varies
S shaped
at higher voltage, temperature higher, so resistance higher and curve flattens

Question 8

Diode IV graph

Answer 8

only increases when voltage higher than 0
like parabola just on positive side

Question 9

thermistor behaviour and R,t graph shape

Answer 9

• as temp increases resistance decreases
• but not linear relationship, graph curved shape

Question 10

Resistivity of wire equation

Answer 10

ρ = RL/A
resistivity = resistance x length / cross sectional area

at constant temperatures

Question 11

Area of circle using diameter

Answer 11

A = π(d^2)/4

Question 12

semiconductors

Answer 12

• some electrons still bounded to material
• when it gets hotter, electrons are liberated
• so more charge carriers freed
• so resistance decreases

thermistors (negative temp coefficient) work like this

Question 13

temperature vs resistance relationship in most materials

Answer 13

as t increases, more vibrations and collisions
harder for electrons to pass through
resistance increases

Question 14

superconductivity and uses

Answer 14

a property of materials where R drops to zero below a certain critical temperature

used in
- reducing energy loss in transmission of electrical power
- making strong magnetic fields

Question 15

Kirchhoff’s laws

Answer 15

1) current flowing into a junction is equal to current flowing out of it
(conservation of charge)

2) the sum of the emfs is equal to the sum of the p.ds in a closed loop
(conservation of energy)

Question 16

ε emf (electro motive force)

Answer 16

work done per unit charge transferring energy into electrical energy

Question 17

V potential difference

Answer 17

work done per unit charge transferring energy from electrical energy

Question 18

Resistors in series and prove

Answer 18

Rt = R1 + R2 + …

Vt = V1 + V2 + …
ItRt = I1R1 + I2R2 + …
I is constant in series
Rt = R1 + R2 + …

Question 19

resistors in parallel

Answer 19

1/Rt = 1/R1 + 1/R2 + …

It = I1 + I2 + …
Vt/Rt = V1/R1 + V2/R2 + …
V is constant in parallel
1/Rt = 1/R1 + 1/R2 + …

Question 20

power, current, voltage

Answer 20

P = IV

Question 21

Power, current resistance

Answer 21

P = I^2R

Question 22

power, voltage, resistance

Answer 22

P = v^2/R

Question 23

energy, current, time, voltage

Answer 23

E = ItV

Question 24

Variable resistor symbol

Answer 24

-

Question 25

Battery symbol

Answer 25

-

Question 26

Diode symbol

Answer 26

-

Question 27

Thermistor symbol

Answer 27

-

Question 28

LDR symbol

Answer 28

-

Question 29

LED symbol

Answer 29

-

Question 30

Internal resistance

Answer 30

resistance in the cell

Question 31

emf equation with internal resistance

Answer 31

ε = I(R + r) r is internal resistance R is circuit resistance i.e. ε = V + Ir where Ir are the lost volts therefore V<ε

Question 32

plotting voltage, current on graph to find emf and resistance

Answer 32

ε = I(R + r) V = -rI + ε y = mx + c therefore -r is gradient and ε is y intercept

Question 33

emf for cells in series

Answer 33

εT = ε1 + ε2 +...

Question 34

emf for cells in parallel

Answer 34

εT = ε1 = ε2 = ...