4.1 Electricity: charge and current

Question 1

What is conventional current?

Answer 1

Current that flows from positive to negative.

Question 2

What is electron flow?

Answer 2

Current flow from negative to positive (what’s actually happening).

Question 3

What is electric current?

Answer 3

Current is a net rate of flow of charged particles.

Question 4

What sort of charge flows in electrical current?

Answer 4

Negative charge in the form of electrons.

Question 5

What charge flows in electrolysis?

Answer 5

Positive and negative in the form of ions (positive to cathode, negative to anode).

Question 6

What is electric current measured in?

Answer 6

Amperes (A).

Question 7

What is one coulomb?

Answer 7

The total charge supplied by a current of one ampere in one second.

Question 8

What is the equation for charge?

Answer 8

Charge = current x time (Q=It)

Question 9

What is the charge on one electron?

Answer 9

-1.6x10^-19

Question 10

What is the number of electrons in one coulomb of charge?

Answer 10

6.25x10^18

Question 11

What do like charges do?

Answer 11

Repel.

Question 12

What do opposite charges do?

Answer 12

Attract.

Question 13

What do a charged object and an uncharged object do?

Answer 13

Attract.

Question 14

What is used to measure current?

Answer 14

An ammeter.

Question 15

How are ammeters connected in a circuit?

Answer 15

In series.

Question 16

Why are ammeters connected in series?

Answer 16

They need to measure how many coulombs pass through a point in the wire per second.

Question 17

What is current in a series circuit?

Answer 17

The same at any point in the circuit.

Question 18

What is current in a parallel circuit?

Answer 18

Shared between branches.

Question 19

What is Kirchhoff’s first law?

Answer 19

The sum of the currents leaving a point is equal to the sum of the currents entering that point.

Question 20

What is charge carrier density?

Answer 20

The number of free charges per cubic metre.

Question 21

What is mean drift velocity?

Answer 21

The average velocity with which electrons will move down a wire.

Question 22

What is the equation for current (using mean drift velocity)?

Answer 22

Current = charge carrier density x cross-sectional area x charge x mean drift velocity (I=nAqv).

Question 23

What does a good conductor have?

Answer 23

A large value for ‘n’.

Question 24

What does an insulator have?

Answer 24

A value for ‘n’ near to zero.

Question 25

What is the value of ‘n’ in semiconductors?

Answer 25

A million times smaller than in metals.

Question 26

How can the value for ‘n’ be altered?

Answer 26

By adding impurities (doping).

Question 27

Why do conduction electrons travel faster in semiconductors than in conductors?

Answer 27

The value of ‘n’ is smaller so there is a smaller charge carrier density and therefore less resistance.

Question 28

What does increasing the temperature of a metal do?

Answer 28

Increase the vibrations of the ions which will increase the resistivity of the metal and decrease the current because it lowers the drift speed.

Question 29

What does increasing the temperature of a semiconductor do?

Answer 29

Increases the small charge carrier density, so decreases the resistivity (a thermistor).