Topic 4.2 - Electrical Quantities

Question 1

Where are electric fields found?

Answer 1

Around every electric charge.

Question 2

What is an electric field?

Answer 2

A region of space in which the effects of charge can be felt. When another charge enters the field, both charges interact and experience a force

Question 3

Objects with the same charge…

Answer 3

…repel.

Question 4

Objects with opposite charges…

Answer 4

…attract.

Question 5

What is charging?

Answer 5

The addition or removal of electrons from a material.

Question 6

How can charge be detected?

Answer 6

Using a gold leaf electroscope; the gold leaf is repelled by positive charge or attracted to negative charge.

Question 7

What is charging by induction?

Answer 7

When a charged object is brought near to a conductor, attracting/repelling electrons in the conductor and causing a net charge to develop in the conductor as a result of electron distribution

Question 8

What is a conductor?

Answer 8

A conductor is a material which can conduct electricity; electrons are able to flow through it.

Question 9

What is an insulator?

Answer 9

An object which does not conduct electricity. Electrons cannot flow through the material.

Question 10

How is static electricity produced?

Answer 10

When two insulators are rubbed together, transferring electrons, to form a positive and a negative charge.

Question 11

What is an electric current?

Answer 11

Current is the rate of flow of charge in an electric circuit.

Question 12

What is required in order for charge to flow?

Answer 12

• A potential difference
• A closed circuit

Question 13

Describe the value of current across a circuit

Answer 13

• Current is the same at any point in a closed series circuit.
• Current is split between the branches of a parallel circuit.

Question 14

Give an equation linking charge and current, giving SI units

Answer 14

Charge (C) = current (A) x time (s)

Question 15

How is current measured?

Answer 15

Using an ammeter, wired in series to the circuit.

Question 16

What is conventional current?

Answer 16

Conventional current (used in circuit diagrams etc.) represents the flow of positive charge; it flows in the opposite direction to the flow of electrons.

Question 17

What is EMF?

Answer 17

Electromotive force (the voltage supplied by a power source).

Question 18

What are the units of EMF?

Answer 18

Volts, V.

Question 19

Define EMF in terms of energy

Answer 19

The energy supplied by the source per unit charge around the circuit.

Question 20

What are the units of potential difference?

Answer 20

Volts, V.

Question 21

Define potential difference

Answer 21

The work done per unit charge flowing between any two points.

Question 22

How is potential difference measured?

Answer 22

Using a voltmeter, wired in parallel.

Question 23

What is 1V equivalent to?

Answer 23

1 Joule per Coulomb (1 JC−1)

Question 24

Give an equation linking current and potential difference, giving all SI unitsp.d. (V) = current (A) x resistance (𝝮)

Answer 24

p.d. (V) = current (A) x resistance (𝝮)

Question 25

How does resistance affect the current flowing through a circuit?

Answer 25

The larger the total resistance in the circuit, the smaller the current will be.

Question 26

Draw the IV characteristic of an ohmic conductor

Answer 26

Question 27

Draw and explain the IV characteristic of a filament lamp

Answer 27

When current flows, the filament produces heat. This increases the resistance of the filament (R=V/I)

Question 28

How does resistance relate to the length of a wire?

Answer 28

Resistance increases with length.

Question 29

How does resistance relate to the cross sectional area of a wire?

Answer 29

Resistance decreases as cross sectional area increases (they are inversely proportional).

Question 30

How is energy transferred in a circuit?

Answer 30

From the battery/power source to the circuit components, and dissipated into the surroundings as heat.

Question 31

What factors affect the energy transferred when charge flows through a component?

Answer 31

• Amount of charge
• The potential difference across the component