Charge and Current

Question 1

Define Electric Current in words.

Answer 1

Electric Current is the rate of flow of charge passed through a fixed point

Question 2

State the equation that defines electric current.

Answer 2

Change in charge over Change in time

Question 3

One Ampere (1A) is the same as…

Answer 3

1 Coloumb per second

Question 4

What is electrc charge?

Answer 4

A physical property which can either be positive or negative. Opposite charges attract whilst like charges repel.

Question 5

Define Coloumb

Answer 5

The charge that flows past a point in one second when there is a current of 1 Amp

Question 6

What is the elementary charge, e?

Answer 6

-1.6x10-19C

Question 7

What is the relative charge of a Proton?

Answer 7

+1

Question 8

How does an object become charged?

Answer 8

When electrons are transferred to or from the object

Question 9

What is meant by quantised charge?

Answer 9

The principle that the charge of any object is an integer multiple of the elementary charge

Question 10

What are the charge carriers of metal?

Answer 10

Electrons

Question 11

How can you produce an electric current in a metal wire

Answer 11

By moving a metal wire throguh a magnetic field

Question 12

What is conventional current?

Answer 12

Conventional Current is the direction the positive charge flows.

Question 13

What is the name given to liquids with conduct electricity

Answer 13

Electrolyte

Question 14

What are the charge carriers in a liquid?

Answer 14

Mobile electrons and ions

Question 15

What are cations and anions?

Answer 15

Cations are ions that are positively charged. Anions are ions that are negatively charged.

Question 16

What is an Cathode?

Answer 16

The cathode is the positive charge or oxidizing elctrode that acquires electrions from external circut and is reduced during electrochemical reactions.

Question 17

What is an Anode?

Answer 17

An anode is the negative or reducing electrode that releases electrons to external circuts and oxidizes during electrochemical reactions.

Question 18

What instrument is used to measure current?

Answer 18

An ammeter

Question 19

What is meant by conservation of charge?

Answer 19

Conservation of charge is the principle that the total electric charge in an isolated system that never changes.

Question 20

State Kirchoff’s first law

Answer 20

Kirchoff’s first law states that the current flowing into a junction are equal to the sum of the circuts out of the same junction ( I in = I out)

Question 21

What is number density?

Answer 21

Number of partcular object or species per unit volume

Question 22

What are the units of number density?

Answer 22

m-3 or cm-3

Question 23

Describe the motion of electrons in a wire as they move towards the positive terminal of the supply.

Answer 23

Electrons flow from the negative terminal to the positive terminal.

Question 24

Describe the motion of electrons in an unconnected wire.

Answer 24

The electrons will collide with each other and move in random directions.

Question 25

Define mean drift velocity.

Answer 25

The average velocity with which free electrons in a conductor can get drifted under the influence of an external electric field applied across a conductor.

Question 26

Explain what happens to the mean drift velocity of charge carriers when the cross sectional area of wire reduces.

Answer 26

The average velocity will decrease, and less electrons will flow causing reistance.