12.1 Current and Charge

Question 1

What must be true of a circuit for an electric current to pass round

Answer 1

It must be complete and there must be a source of potential difference such as a battery

Question 2

What is the electric current

Answer 2

The rate of flow of charge in the wire or component

Due to the passage of charged particles called charge carriers

Question 3

What are the charge carriers in metals

Answer 3

Conduction electrons

They move about inside the metal, repeatedly colliding with each other and the fixed positive ions in the metal

Question 4

What carries the charge when an electric current is passed through a salt solution

Answer 4

Ions, which are charged atoms or molecules

Question 5

Simple test for conduction of electricity

Answer 5

Meter, cell and test material. Meter shows non-zero reading whenever any conducing material through the conducting material and causes them to pass through battery and meter.

Question 6

What is the convention for the direction of current in a circuit

Answer 6

From positive to negative

Question 7

What is the unit of current

Answer 7

Ampere (A)

Defined in terms of magnetic force between two parallel wires when they carry the same ccurrent

Question 8

What is the symbol of current

Answer 8

I

Question 9

What is the unit of charge

Answer 9

Coulomb (C)

Equal to the charge flow in one second when the current is one ampere

Question 10

What is the symbol of charge

Answer 10

Q

Question 11

For a current I, the charge flow ΔQ in time Δt is given by…

Answer 11

ΔQ = IΔt

Question 12

What is the charge flow for a current of 1A

Answer 12

10C

Question 13

What is the charge flow for a current of 5A in 200s

Answer 13

1000C

Question 14

What is the charge flow for a current of 10mA in 500s

Answer 14

5C

Question 15

For a charge flow ΔQ in a time interval Δt, the current I is given by…

Answer 15

I = ΔQ/Δt

Question 16

A current of 1A along a wire must be due to…

Answer 16

…6.25*10^18 electrons passing along the wire each second

Question 17

In an insulator, each electron is attached to an ______ and cannot move away from the atom. When a voltage is applied across the insulator, ___ ______ passes through the insulator because ___ electrons can ______ through the insulator

Answer 17

Atom
No current
No
Move

Question 18

In a metallic conductor, most electrons are ______ to atoms but some are ______ - the delocalised electrons are the ______ ______ in the metal. When a voltage is applied across the metal, these conduction electrons are attracted towards the ______ terminal of the metal.

Answer 18

Attached
Delocalised
Charge Carriers
Positive

Question 19

In a semiconductor, the number of charge carriers ______ with an increase of temperature. The resistance of a semiconductor therefore ______ as its temperature is raised. A pure semiconducting material is referred to as an ______ semiconductor because conduction is due to electrons that ______ ______ from the atoms of the semiconductor.

Answer 19

Increases
Decreases
Intrinsic
Break free

Question 20

How is the human genome mapped

Answer 20

Fragments of DNA are tagged with amino acid bases. Each tagged fragment carries a negative charge. A voltage is applied across strip of gel with spot of liquid containing fragments which are attracted to + electrode. Smaller fragment, faster it moves so they separate out according to size. Pass through spot of laser light causing a dye attached to each tag to fluoresce. Computer works out display