Electricity

Question 1

Define current

Answer 1

It is the rate of flow of charge

Question 2

What is Kirchhoff’s first law

Answer 2

That the sum of the currents entering in a junction is equal to the sum leaving the junction

Question 3

What is the distinction between conductors, semi conductors and insulators in terms of n

Answer 3

Conductors have the greatest number density followed by semi conductors, then insulators.

Question 4

Define emf

Answer 4

Work done on charge carriers per unit charge

Question 5

Define p.d.s

Answer 5

Is energy transferred from electrical energy to other forms per unit charge

Question 6

What is Kirchhoff’s second law

Answer 6

Sum of emf = sum of p.d.s around a closed loop

Question 7

What are the energy transfer equations

Answer 7

W=VQ W=ξQ eV=0.5mv²

Question 8

What is ohms law

Answer 8

Current is directly proportional to p.d.s when there is a constant temperature

Question 9

What is the I-V characteristics of a resistor

Answer 9

Resistance is constant

Question 10

What is the I-V characteristic of a filament lamp

Answer 10

As current increases so does temperature, increasing resistance

Question 11

What is the I-V characteristic of a diode

Answer 11

Current only flows in one direction. Resistance decreases when currents increases.

Question 12

What is the I-V characteristics of a thermistor

Answer 12

As temperature increases resistance decreases

Question 13

What happens to resistance when length increases

Answer 13

Length is directly proportional to resistance. If length doubles so will resistance.

Question 14

What happens to resistance when area increases

Answer 14

Area is inversely proportional to resistance. If area doubles resistance will half.

Question 15

How does resistance vary in an LDR

Answer 15

As light intensity increases resistance decreases

Question 16

Equation for resistivity

Answer 16

ρ=RA/l measured in ohm meters

Question 17

To find resistivity of a metal

Answer 17

1. Find the area of the wire using a micrometer to find the diameter.
2. Create a circuit with the test wire being attached to a ruler.
3. Using crocodile clips vary the length of the wire recording current and voltage. Get repeats and do this for different lengths.
4. Then work out resistance and plot a resistance against length graph
5. The gradient will be ρ/a.

Question 18

How does temperature effect resistivity

Answer 18

As temperature increases resistivity increases

Question 19

Equations for electrical power

Answer 19

P=VI
P=I²R
P=V²/R

Question 20

Energy transfer equation

Answer 20

W=VIt

Question 21

What is a kilowatt-hour

Answer 21

Is a unit of energy calculating cost of energy

Question 22

How calculate resistance in series

Answer 22

R=R1 + R2 + …

Question 23

How to calculate resistance in parallel

Answer 23

1/R= 1/R1 + 1/R2 + …

Question 24

What is internal resistance

Answer 24

It is resistance inside the battery from electrons colliding with atoms.

Question 25

What is lost volts

Answer 25

It is the difference between between emf and terminal p.d.s

Question 26

Equations for emf

Answer 26

ε=I(R+r)

ε=V+Ir

Question 27

How to determine internal resistance

Answer 27

• Vary the circuit by changing the value of the variable resistor and measure p.d. And current at different values.
• Plot a V against I graph
• rearrange to give V=-rI+ε
• emf is the y intercept and -r is the gradient

Question 28

What are potential divider equations

Answer 28

Vout=(R2/R1+R2)xVin

V1/V2=R1/R2

Question 29

What is a potentiometer

Answer 29

A potentiometer has a variable resistor to vary the voltage using a slider or knob. This adjusts the relative sizes of R1 and R2.

Question 30

How to investigate potential divider

Answer 30

You can make a potential divider using an LDR or a thermistor.

Set up equipment with a fixed resistor and a variable resistor such as an LDR. You should measure Vout across the LDR as you change light intensity and plot a graph.