2.1 Conduction of electricity

Question 1

What is electrical current?

Answer 1

rate of flow of charge

Question 2

What is conventional current?

Answer 2

the flow of a positive charge from positive to negative and is the reverse of real electron flow

Question 3

What is electron flow?

Answer 3

the flow of a negative charge from negative to positive

Question 4

How to work out current?

Answer 4

current = change in charge ÷ change in time

I (amps) = △Q (coulombs) ÷ △T (seconds)

Question 5

How to work out the change in charge?

Answer 5

change in charge = current x change in time

△Q = I x △T (ONLY WORKS WHEN CURRENT IS CONSTANT)

Question 6

How to work out the change in time

Answer 6

change in time = change in charge ÷ Current

△T = △Q ÷ I

Question 7

What is the total charge in a current - time graph?

Answer 7

Area under the line

Question 8

In metals, what does electrons do?

Answer 8

they move to make a current

Question 9

What is the charge of one electron?

Answer 9

1.6 x 10⁻¹⁹ coulombs

Question 10

Q. A current of 2.4 amps. How many electrons have flowed past a point in 5 minutes?

Answer 10

5 mins = 300 seconds
△Q = I x △T
       = 2.4 x 300
       = 720 coulombs
number of electrons = 720 ÷ 1.6 x 10 ^ -19
= 4.5 x 10^21

Question 11

What is electric current?

Answer 11

Rate of flow of charge

Question 12

How to work out number of electrons?

Answer 12

charge (C) ÷ 1.6 x 10⁻¹⁹

Question 13

What is the unit of battery capacity?

Answer 13

Ah (amp hours)

Question 14

What does a battery of 70Ah means?

Answer 14

the battery can supply 1 amp for 70 hours, or 2 amps for 35 hours, or 10 amps for 7 hours… It has a battery capacity of 70 x 3600 = 252000 C per hour.

Question 15

What is drift velocity?

Answer 15

the average velocity attained (gained) by charged particles (e.g electrons)

Question 16

what is drift velocity measured in?

Answer 16

ms⁻¹ meters per seconds

Question 17

What is the pre condition for the electrons to move with a drift velocity?

Answer 17

When a potential difference(voltage) is applied across the wire.

Question 18

How to calculate volume of a wire?

Answer 18

Avt m³

A = cross sectional area[m²] (π r²)
vt = distance [m] (velocity x time)

Question 19

How to calculate the number of electrons?

Answer 19

nAvt

n = number of free electrons per m³
Avt = volume (m³)

Question 20

How to calculate the charge in the volume?

Answer 20

nAvte

n = number of free electrons
Avt = volume
e = the charge of an electron [1.6 x 10⁻¹⁹] C

Question 21

How to calculate the current?

Answer 21

Current = nAvte ÷ t ( change in charge ÷ change in time)
both t cancels each other, therefore
Current = nAve

Question 22

How to calculate drift velocity?

Answer 22

V = I ÷ Ane

Question 23

Does the current change in the narrow section?

Answer 23

No, Current is the rate at which electric charge flows past a point, meaning that it doesn’t get used up by components therefore always stays the same.

Question 24

Does the velocity change in the narrow section?

Answer 24

Yes, velocity is inversely proportional to area,

V ∝ 1 / A meaning that the bigger the area, the smaller the velocity and vice versa