Electric Circuits

Question 1

Define current

Answer 1

Rate of flow of charge

Question 2

What does the gradient on a charge-time graph tell us?

Answer 2

Current
I = Q/t

Question 3

How to you work out charge from a current-time graph?

Answer 3

The area under the graph
Q= It

Question 4

An ammeter must…

Answer 4

have a low resistance and must be placed in series

Question 5

A voltmeter must…

Answer 5

have infinitely high resistance and must be placed in parallel

Question 6

Another word for voltage is…

Answer 6

EMF/potential difference

Question 7

Potential difference is…

Answer 7

A measure of the amount of energy or unit of charge transferred between 2 points in a circuit

Question 8

What is Kirchoff’s first law?

Answer 8

The total current flowing into a point is equal to the current flowing out of a point.
Conservation of Charge

Question 9

What is Kirchoff’s second law?

Answer 9

Around any closed loop in a circuit, the sum of the p.d across all components is the p.d of the supply.
Conservation of Energy

Question 10

Define power

Answer 10

The rate of work done

Question 11

1 watt of power means…

Answer 11

1 joule of energy is used every second

Question 12

State Ohm’s Law

Answer 12

V = IR
at a constant temperature

Question 13

In a series circuit the current is…

Answer 13

the same across all components

Question 14

In a parallel circuit the current is…

Answer 14

Total current = the sum of the current in all branches

Question 15

Potential difference in a series circuit…

Answer 15

total p.d is split up across all components, in the ratio of their resistance

Question 16

Potential difference in a parallel circuit is…

Answer 16

the same across each brach
p.d across each branch = p.d of source

Question 17

Resistance in a series circuit…

Answer 17

total resistance = the sum of the resistance in all the components

Question 18

Resistance in a parallel circuit…

Answer 18

Reciprocal of Resistance = the same of all the reciprocals of the resistance of all the components
1/RT = 1/R1 + 1/R2 + 1/R3 …

Question 19

Is a resistor a conductor?

Answer 19

Yes - it is a conductor so current can still flow around a circuit however resists let less current flow

Question 20

What effects the resistance of a resistor?

Answer 20

CSA of the wire
Length of the wire
Material of the wire (resistivity)
Temperature of the wire

Question 21

What is resistance proportional to?

Answer 21

Length

Question 22

What is resistance inversely proportional to?

Answer 22

CSA

Question 23

What is the Resistivity of a material?

Answer 23

The resistance of a 1m^2 long sample (the resistance per unit cube)
It is a property of a material

Question 24

The resistivity is constant if…

Answer 24

the temperature is constant

Question 25

What is the conductivity?

Answer 25

1/resistivity

Question 26

On a resistance-length graph, what pattern does the graph follow?

Answer 26

positive straight gradient

Question 27

On a resistance-length graph, what does the gradient tell you?

Answer 27

resistivity/area

Question 28

What does a resistance-area graph look like?

Answer 28

A curve getting less steep as it goes down (negative gradient)

Question 29

What does a resistance-1/CSA graph look like?

Answer 29

Positive straight gradient

Question 30

What does the gradient of a resistance-1/CSA graph mean?

Answer 30

It is the resistivity multiplied by the length

Question 31

Prove: 1/RT = 1/R1+ 1/R2 + 1/R3 in parallel

Answer 31

iTotal = i1 + i2 + i3 i = V/R hence: v/RT = v/R1 + v/R2 + v/R3 v is constant and therefore: 1/RT = 1/R1 + 1/R2+ 1/R3

Question 32

What is a potentiometer?

Answer 32

A device that provides a p.d ranging from 0v and Vs (supply voltage)

Question 33

Length needed =

Answer 33

length of wire x (voltage out/total voltage)

Question 34

What do the letters stand for in I = nAvq

Answer 34

I = Current (A) v = Drift velocity (ms-1) A = CSA of conductor (m2) n = Charge density (no. of electrons per m3) q = charge on each charge carrier

Question 35

What is the charge density?

Answer 35

the number of charge carriers per m3

Question 36

A poor conductor has ___ charge carriers

Answer 36

few

Question 37

A good conductor has ___ charge carriers

Answer 37

many

Question 38

4V is equivalent to 4J per...

Answer 38

coulomb of charge

Question 39

5ohm resistance means that 5v is required for...

Answer 39

1A of current

Question 40

Vout/Vsupply =

Answer 40

R2 / (R1+R2)