2.2 Resistance

Question 1

Define EMF (electro motive force)
(2-way)

Answer 1

• The energy converted from chemical energy
• to electrical potential energy

Question 1

Define PD (potential difference)

(2 definitions)

Answer 1

The difference in electrical potential energy at 2 different points

The energy converted from electrical potential to other forms

Question 2

PD ≡ ? ≡ ?

Answer 2

≡ V ≡ Jc^−1

Question 3

How to set up V-I characteristics investigation?
(What 5 items u need?)

Answer 3

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

Question 4

Purpose of variable resistor within investigation?
+ alternate?

Answer 4

Changes resistance ∴ change voltage + current

Can use variable power supply

Question 5

Define ohm and his law
(law = 2-way)

Answer 5

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

Question 6

Dw about formulas, provided in booklet

Answer 6

Yipee

Question 7

How does resistance work?
(3 step by steps which are weirdly long…?)

Answer 7

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 8

Derivations of resistivity?
(4 step by steps although check up… look at the og book)

Answer 8

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 9

Define power and it’s power…. (unit)

Answer 9

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

Question 10

Definition of resistivity?
(2-way)

Answer 10

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

Question 11

Course, here’s the symbols for resistivity equation

Answer 11

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

Question 12

Resistance if temperature is high in wire?
(4 step by steps)

Answer 12

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

Question 13

Resistance if temperature is low in wire?
(3 step by steps… light sonority)

Answer 13

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

Question 14

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

Answer 14

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

Question 15

What’s a super conductor?
(2-way)

Answer 15

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

Question 16

What’s a transition temperature?
(2-way)

Answer 16

• A temperature for when their resistance
• drops rapidly to zero

Question 17

3 uses of super conductors?

Answer 17

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

Question 18

How does it work for the maglev train?
(3 step by steps)

Answer 18

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