2. Resistance

Question 1

dDefine EMF (electro motive force)

Answer 1

The energy converted from chemical energy to electrical potential energy

Question 2

Define PD (potential difference)

(2 definitions)

Answer 2

The difference in electrical potential energy at 2 different points

The energy converted from electrical potential to other forms

Question 3

PD ≡ ? ≡ ?

Answer 3

≡ V ≡ Jc^−1

Question 4

How to set up V-I characteristics investigation?

Answer 4

Items needed and in order:
- Cell
- Variable resistor
- Voltmeter (above or below the following things:)
- Bulb & resistor
- Ammeter

Question 5

Purpose of variable resistor within investigation?
+ alternate?

Answer 5

Changes resistance ∴ change voltage + current

Can use variable power supply

Question 6

Define ohm and his law

Answer 6

• Unit of resistance Ω
• At constant temperature
• Current in wire proportional to P.D. across it

Question 7

Dw about formulas, provided in booklet

Answer 7

Yipee

Question 8

Define power and it’s power

Answer 8

• The rate of doing work
• Measured in Watts (W) or Js^-1

Question 9

How does resistance work?

Answer 9

1. Free electrons move thru wire, collision with atoms + each other = slows them down
2. Energy transferred to atoms, vibrate more = becomes hotter
3. Harder for electrons to flow = resistance

Question 10

Derivations of resistivity?

Answer 10

1. Length of wire proportional to resistance (R ∝ L)
2. Area increases = resistance decreases proportionally (inversely proportional)
   R ∝ 1/A
3. Combination = R ∝ L/A
4. Constant for ^^ = resistivity
   R/L = ρ/A
   tangible type shi

Question 11

Definition of resistivity?

Answer 11

The general measurement of how much a material resists the flow of current

Question 12

Course, here’s the symbols for resistivity equation

Answer 12

ρ = resistivity
R = resistance
A = cross sectional area
L = length

Question 13

Resistance if temperature is high in wire?

Answer 13

1. Positive ions vibrate at greater amplitudes
2. Electron-ion collisions more frequent
3. Flow of electrons slowed = current reduced
4. Resistance high

Question 14

Resistance if temperature is low in wire?

Answer 14

1. Electrons pass positive metal ions with ease
2. Due to fewer collisions
3. Resistance is low

Question 15

In semi conductors, resistivity is different to normal conductors (temperature), tell me about it?

Answer 15

1. More electrons break free of their atoms
2. Increase in number of electrons available for conduction
3. Resistivity decreases

Question 16

What’s a super conductor?

Answer 16

A material with 0 electrical resistance between absolute zero - liquid nitrogen temps (77k)

Question 17

What’s a transition temperature?

Answer 17

A temperature for when their resistance drops rapidly to zero

Question 18

3 uses of super conductors?

Answer 18

1. Maglev train
2. MRI scanner
3. Particle accelerators

Question 19

How does it work for the maglev train?

Answer 19

1. Produces super strong magnetic field
2. Makes train levitate off track
3. no resistance = greater speeds