8.1 Electric charge

Question 1

What does ‘quantised’ mean?

Answer 1

Fundamental particles have charges of fixed value

Question 2

What is the elementary charge?

Answer 2

1.6 x 10^-19

Question 3

What is the formula for electric current?

Answer 3

I = change in q/change in t

Question 4

Unit for charge

Answer 4

Coulomb

Question 5

Unit of current

Answer 5

Ampere

Question 6

How does current in metals behave?

Answer 6

Temperature increases = frequency of vibrations increase = electrical resistance increases

Question 7

What direction does conventional current move in?

Answer 7

From + to -

Question 8

What direction do electrons flow in?

Answer 8

From - to +

Question 9

How does current behave in electrolytes?
use the example of sodium chloride

Answer 9

• Electrolytes are molten ionic compounds in which ions are free to move
• In sodium chloride, common salt dissolved in water separates into Na+ and Cl- ions.
• Na+ cations attracted to -cathode, Cl- anions are attracted to +anode
• On reaching anode, Cl- releases an electron that flows through the metal part of the circuit
• In the cathode, electrons combine with the Na+ ions

Question 10

How do you measure current?
Where should the component be placed?

Answer 10

• An ammeter
• In series, because it has low resistance so it would create a short circuit

Question 11

What is conservation of charge?

Answer 11

Electric charge can neither be created nor destroyed. In any closed system, the total amount of charge is constant

Question 12

What is Kirchhoff’s 1st Law?

Answer 12

the total of the currents entering a point must equal the total of the currents leaving the point

Question 13

How do you increase current?

Answer 13

• Increase the number of charge carriers passing the point (e.g. using a wire with a bigger cross-sectional area)
• Increase the speed of the charge carriers so more pass every second

Question 14

What is number density?

Answer 14

The number of free electrons per unit volume