Electrcity

Question 1

Circuit calculation steps

Answer 1

1: Work out total resistance using Rₜ = R₁ + R₂ and 1/Rₜ = 1/R₁ + 1/R₂
2: Work out total current V=IR
3: Use kirchhoff’s laws to work out volatge
Branches: Iₐ = I x R₈/Rₐ + R₈ and I₈ = I x Rₐ/Rₐ+R₈

Question 2

Potential Divider equation

Answer 2

Vₒᵤₜ = R₂ x Vᵢₙ/R₁ + R₂

Question 3

Define electric current

Answer 3

The rate of flow of charge and current

Current = charge/time

Question 4

Define potential difference

Answer 4

The work done when one coulomb of charge is moved between two points in a circuit
PD = work done / charge

Question 5

Define resistance

Answer 5

The ratio of the voltage across a component to the current flowing through it
resistance = voltage / current

Question 6

What are the equations for electrical energy

Answer 6

E = ItV
E = Pt

Question 7

State Ohms law

Answer 7

The current flowing through a metallic conductor is directly proportional to the potential difference applied across it at constant temperature

Question 8

What does the gradient of an I-V graph represent

Answer 8

1 divided by the resistance

Question 9

Define resistivity

Answer 9

A measure of how easily a material conducts electricty

Question 10

What is a superconductor

Answer 10

A material that has 0 resistivity below a certain temperature

Question 11

What is the unit of resistivity

Answer 11

Ωm

Question 12

How does a LDR work?

Answer 12

A light dependent resistors resistance changes based on light intensity. As the light intensity increases resistance decreases

Question 13

How does a thermistor work

Answer 13

Resistance changes based on temperature. As the temp increases resistance decreases

Question 14

What are the rules for a series circuit

Answer 14

Current is the same and voltage is split

Question 15

What are the rules for parallel circuits

Answer 15

Current is shared and voltage is the same

Question 16

What does Kirchoffs first law state

Answer 16

The total current into a junction is equal to the total current out of a junction

Question 17

What does Kirchoffs second law state

Answer 17

The sum of EMFs around the loop is equal to the sum of the potential drops around the loop

Question 18

Resistance in series

Answer 18

RT = R1 + R2

Question 19

Resistance in parallel

Answer 19

1/RT = 1/R1 + 1/R2

Question 20

What is a potential divider

Answer 20

Consists of two or more resistors in series and with a source of fixed potential difference (to produce aa
required PD)

Question 21

How does a potential divider work

Answer 21

A potential divider uses resistors to dissipate energy and therefore reduce the work done per unit charge or the voltage output

Question 22

Examples of potential dividers

Answer 22

Light dimmers and volume control

Question 23

Define electromotive force (EMF)

Answer 23

The amount of energy transferred by a cell per unit charge that passes through it

Question 24

What is internal resistance

Answer 24

The loss of potential energy per unit charge in the source when a current passes through it

Question 25

If you plot voltage against current in the equation for emf what does the gradient represent

Answer 25

NEGATIVE internal resistance