Current & Charge

Question 1

What is required to make an electric current pass around a circuit?

Answer 1

• Complete Circuit

* Source of potential difference ( e.g. a battery ).

Question 2

What is electric current?

Answer 2

The rate of flow of charge in the wire or component.

Question 3

What is the current?

Answer 3

• Rate of flow of charge

* Current is due to the passage of charged particles ( called charge carriers ).

Question 4

What are the charge carriers inside metals?

Answer 4

• The charge carriers are conduction electrons.

Question 5

What is the behaviour of charge carriers inside metals?

Answer 5

• They move about inside the metal

* Repeatedly colliding with each other and fixed positive ions in the metal

Question 6

What carries the charge through a salt solution?

Answer 6

• Charge is carried by ions

Question 7

What are ions?

Answer 7

Charged atoms or molecules.

Question 8

What is the test for conduction of electricity?

Answer 8

• Connect cell to a meter and test material via metal clips, and connect the meter to the test material.
• The meter shows a non zero reading whenever any conducting material is connected to the circuit.
• Battery forces the charge carriers through the conducting material and causes them to pass through the battery and the meter.
• If test material is a metal, the charge carriers in all parts of the circuit are electrons.

Question 9

What is the conventional direction of current?

Answer 9

Positive to negative

Question 10

What is the unit of current?

Answer 10

Ampere ( A )

Question 11

What is the definition of an ampere?

Answer 11

Magnetic force between two parallel wires when they carry the same current, symbol I.

Question 12

What is the unit of charge?

Answer 12

Coulomb

Question 13

What is coulomb defined as?

Answer 13

Amount of charge that passe in 1 second if the current is 1 ampere ( A ).

Question 14

How can you measure the current flowing through a part of a circuit?

Answer 14

Using an ammeter

Question 15

What is the formula for the flow of charge?

Answer 15

ΔQ = I x Δt

Charge flow = Current * Change in Time

Question 16

For a charge flow in time, t, what is the formula for current?

Answer 16

I = ΔQ / Δt
t = time
Q = charge

Question 17

How must an ammeter be connected in a circuit to be used?

Answer 17

• In series

* This is to make sure that the current through the ammeter is same as the current through the component.

Question 18

What are the three terms which materials can be classified as?

Answer 18

• Semi Conductor
• Insualtor
• COnductors

Question 19

How are electrons present in insulators?

Answer 19

• Each electron is attached to an atom and cannot move away from the atom.

Question 20

What happens when voltage is applied across an insulator?

Answer 20

• No current passes through the insulator
• This is because no electrons can move through the insulator, due to each electron being attached to an atom, and not able to move away from the atom.

Question 21

How are electrons present in metallic conductors?

Answer 21

Most electrons are attached to atoms but some are delocalised.

Question 22

What are the charge carriers in metals?

Answer 22

De-localised electrons.

Question 23

What happens when a voltage is applied across a metal?

Answer 23

• When a voltage is applied across the metal, conduction electrons are attracted towards the positive terminal of the metal.

Question 24

How do semi conductors work?

Answer 24

• Number of charge carriers increases with an increase of temperature.
• Resistance therefore decreases as its temperature is raised.

Question 25

What is a pure semi conducting materiel?

Answer 25

• Intrinsic semi conductor.

* This is because conduction is due to electrons that break free from the atoms of the semi conductor.

Question 26

How does resistance vary with changing temperatures in semi conductors?

Answer 26

As the temperature increases, resistance decreases.