Heating effects of current + Electric resistance + electric power

Question 1

Formula for relationship between speed and area

Answer 1

A₁V₁ = A₂V₂

Question 2

How does current produce heat in a conductor?

Answer 2

1. Electric field accelerates electrons in conductor
2. Electrons gain kinetic energy
3. Have inelastic collisions with metal atoms, losing energy to them
4. Electric field again accelerates electrons till next collision;process repeats
5. Electrons keep providing energy to metal atoms
6. Atoms vibrate about equilibrium positions with increased KE

Question 3

Electric resistance

Answer 3

Opposition to flow of electric current

Question 4

Ohm’s law in words

Answer 4

Current through a conductor is directly proportional to p.d. across it provided temperature is constant

Question 5

Ohm’s law formula

Answer 5

V=IR

Question 6

Graph of I vs V for ohmic material?

Ohmic=obeys Ohm’s law

Answer 6

Straight line passing through origin

Question 7

Example of ohmic material?

Answer 7

Filament bulb when current is very small

Question 8

What happens as current in filament bulb increases?

Answer 8

Temperature of filament increases, increasing resistance . Bulb now non=ohmic

Graph still passes through origin

Question 9

Two more examples of non-ohmic materials

Answer 9

Diode
Thermistor

Question 10

What happens to resistance as I increases?

Answer 10

R increases

Question 11

3 factors affecting resistance of wire at constant temperature

Answer 11

1. Nature of material
2. Length of wire(L)
3. Cross-sectional area(A)

Question 12

Electric resistance R at fixed temperature is directly propotional to length and inversely propotional to A. Formula?

Answer 12

R=p(L/A)

p=resitivity. Depends on material of conductor and temperature

Question 13

2 Formulas for electric power

Answer 13

P=IV
P=I²R = V²/R