Current, Potential difference & Resistance

Question 1

Current - I (A)

Answer 1

Flow of electrical charge (flow of charged particles) (circuit must have p.d for electrical charge to flow)
Size of current is rate of flow of electrical charge
Not used up in a circuit (same current returns to cell as leaves it)

Question 2

Series

Answer 2

Same current all way round circuit
Total p.d of supply is shared between components - adds up to cell p.d (Total energy carried by current is shared)
Resistance adds up - current can’t bypass any resistor

Question 3

Parallel

Answer 3

Current in branches adds up to total current leaving cell
P.d across each branch is the same
Total resistance is less than resistance of smallest resistance

Question 4

Electrical Current

Answer 4

Negative end of cell to positive end / Conventional current: positive end to negative end

Question 5

Potential Difference V (v)

Answer 5

Energy transferred for each coulomb of charge (1 volt is 1 joule energy transferred)

Question 6

Potential Difference V (v)

Answer 6

Energy transferred for each coulomb of charge (1 volt is 1 joule energy transferred)
(The energy transferred when electrons flow)

Question 7

Charge Q (c)

Answer 7

Current of 1 ampere = 1 coulomb of charge flowing per second
Charge is the charge of the electrons in the current
The size of the electrical current is the rate of flow of electrical charge - Q = I x T

Question 8

Resistance R (Ohmic symbol)

Answer 8

Opposition to flow of current - Tells us how much p.d. (energy) is required to drive a current through a component
V = IR - Greater resistance across component - smaller current flow through the component (for a given p.d. across component)
For some components, when current through them changes, resistance changes too

Question 9

Ohmic conductors

Answer 9

Ohmic conductors have constant resistance
Resistance of ohmic conductors doesn’t change with current
At constant temp, current flowing through ohmic conductor is directly proportional to p.d across it (R constant in V = IR) so has straight line I-V characteristic

Question 10

Factors that affect resistance

Answer 10

Components in series or parallel, length of wire, temperature of conductor, thickness of wire

Question 11

Investigating factors affecting resistance method

RP 3

Answer 11

Circuit: Test wire on m ruler. Ammeter connected in line with test wire, voltmeter connected across test wire, crocodile clips on test wire (1 at 0cm, other varies)

1. Attach 2nd clip, record distance between clips with ruler, record current on ammeter, p.d. on voltmeter
2. Move 2nd clip, record everything, repeat

Question 12

Investigating factors affecting resistance data

RP 3

Answer 12

Work out resistance with data using R = V/I, plot graph. Straight line through origin (resistance d.p to length)

Wire heats up - increase resistance. Use small p.d, open switch between reading so wire can cool
Make sure wire is straight - accurate measurements

Could also measure resistance with thickness of wire with setup

Question 13

I-V Characteristics

Current-Potential graphs

Answer 13

Shows how current varies as p.d changes across component. Ohmic conductors have I-V characteristics with straight lines (aka linear components)
Non-linear have curved I-V characteristics - resistance changes depending on current

Question 14

Finding components I-V characteristics

RP 4

Answer 14

Circuit: Component, voltmeter connected across component, ammeter connected in line with component, variable resistor

1. Vary resistance of variable resistor. Alters current flowing through circuit, p.d. across component.
2. Record p.d for that value of current, repeat same reading to get mean.
3. Swap wires connected to battery to reverse direction of current. Measure negative values of current, p.d as well
4. Plot graphs

Question 15

Filament Lamps

Answer 15

Fixed resistor (wire length) is ohmic conductor so test with different resistors - will result in straight lines with different slopes

Filament Lamps: Charge flows through, some energy -> thermal store of filament, heats up & glows. Resistance increases with temperature - less current flows per unit p.d so graph gets shallower

Question 16

Diodes

Answer 16

Current can only pass through in 1 direction (v. high resistance in other direction). Current increases as p.d increases in forward direction - useful for controlling flow of current in circuits

LED: Energy efficient source of light

Question 17

Light Dependent Resistor

Answer 17

Resistance decreases as light intensity increases

Night lights, out door lighting

Question 18

Thermistor

Answer 18

Resistance decreases as temperature increases

Thermostats

Question 19

Charge formula

Answer 19

Q = I x T

Question 20

Resistance formula

Answer 20

R = V/I

Question 21

Power formula

Answer 21

P = E/t
P = VI
P = I^2 x R

Question 22

Series formulas

Answer 22

V total = V1 + V2 + …
I1 = I2 = …
R total = R1 + R2

Question 23

Parallel formulas

Answer 23

V1 = V2 = …
I total = I1 + I2 + …
R total = R/n of resistors