Module 4 Electricity: Charge And Current

Question 1

Define volt.

Answer 1

It is the work done per unit of charge.

Question 2

What way should the front face of a diode be placed in a circuit?

Answer 2

The face with the bar in front of the triangle should be towards the negative terminal.

Question 3

What are the 4 types of resistors you should know about?

Answer 3

Resistor,
Variable resistor,
Light dependant resistor
Thermistor.

Question 4

Describe how you would draw a heater in a circuit diagram.

Answer 4

Draw a rectangle and divide it in 4 equal parts, using three lines

Question 5

What does a fuse look like in diagrams?

Answer 5

A resistor with the wire running through it.

Question 6

How do metals permit flow of electricity?

Answer 6

Metals have crystal lattice structures with long neat rows of positive ions and a sea of delocalised electrons in between the positive ions. These free electrons drift slowly along the structure and create a flow of electricity.

Question 7

Define current. Give Units.

Answer 7

It is the rate of flow of charge. The current is one ampere (A) when 1 coulomb of charge passes in one second.

Question 8

How can an atom become positively ionised?

Answer 8

Atoms can lose electrons if a photon or another electron collides with the electrons in the atom, making a cation.

Question 9

What are the charge carriers in an electrolyte solution?

Answer 9

Positive and negative ions.

Question 10

State kirchhoff’s first law.

Answer 10

All charge entering a junction must equal all charge leaving the junction.

Question 11

Will a value of charge on a particle always be divisible by ‘e’?

Answer 11

Yes, as charge always increases in multiples of ‘e’.

Question 12

What is the charge on an up quark and a down quark?

What’s the composition of protons and electrons, regarding quarks.

Answer 12

+2/3 e on an up quark.
-1/3 e on a down quark.

A proton has 2 up quarks and one down quark
An electron has 2 down quarks and one up quark.

Question 13

What is another way to calculate ‘I’ except using I=Q/t?

Answer 13

I=ne, where n is number of charges flowing per second and e is their charge.

Question 14

What’s another way to calculate ‘Q’ except using ‘Q=I x t’

Answer 14

Q=net, where n is the number of charges flowing per second, e is the charge on the particles and t is the time elapsed.

Question 15

What is mean drift velocity of charge and how do you derive it’s formulae?

Answer 15

It is the average velocity of charge when flowing from one end of the wire to the other.
Volume of wire= AxL, where A is cross sectional area and L is length of wire.
Speed = Distance/time
Time= Distance/Speed, t = L/v, where v is the velocity of the charged particles.

Number of charge carriers per unit volume = n
Total charge carriers in the wire = nAL

Total charge in wire = nALe, where e is the charge on one charged particle.

I=Q/t, nALe/L/v, I=nAev
v=I/nAe.

Question 16

Explain the differences between conductors, semiconductors and insulators in terms of charge carriers.

Answer 16

Conductors have a high number density of charge carriers(conduction electrons), per unit volume.

Insulators have a very low number density of charge carriers per unit volume. Some times even zero.

Semiconductors have values in between conductors and insulators.

Question 17

What can you do to semi conductors to increase their conductivity?
What is this method called?

Answer 17

You can add impurities, different atoms, which increase the number density of charge carriers.
This is called doping.

Question 18

What is the motion of delocalised electrons in a metal wire with no pd applied?

Answer 18

It is random and there is no net movement.