Electricity

Question 1

Define a volt

Answer 1

1J of energy converted by coulomb of charge which flows through a component.

Question 2

What relationship defines resistance?

Answer 2

R = V/I

Question 3

Define Ohm’s Law

Answer 3

Under constant physical conditions, including temperature, the current through an ohmic conductor is directly proportional to the potential difference across it.

Question 4

Draw the IV graph for:

1. an ohmic conductor at a constant temp.
2. a fliament lamp
3. an NTC thermistor
4. a diode

Answer 4

1. straight line through origin
2. sin curve
3. sin curve reflected in y=x
4. see picture

Question 5

Define resistivity

Answer 5

The resistance of a sample of a material 1 m long and with a CSA of 1 m².

Question 6

What factors affect resistivity?

Answer 6

• Arrangement of atoms in the structure
• Impurities in the sample
• Temperature

Question 7

What are superconductors and what can they be used for?

Answer 7

• Materials cooled down to a critical temperature which as a result have zero resistivity.
• Used for:
  
  • power cables which transmit electricity without any loss of power
  • producing really strong magnetic fields ( super conductors exclude magnetic fields inside them)

Question 8

How do cells add in series and parallel?

Answer 8

Series:

E_total = E₁ + E₂ + …

Parallel:

E_total = E₁ = E₂ = …

(for identical cells, because current will split evenly between each branch, so emf gained by each bit of charge will be equal)

Question 9

What is the potential divider formula?

Answer 9

V_out = V_s * R₂/(R₁ + R₂)