Resistance. Rheostats
Answers are for parents and teachers.
1
A tungsten wire (ρ = 0.055 Ω·mm²/m) is 2 m long, S = 0.11 mm². R in ohms?
1
2
A nickelin wire 9 m long has a resistance of 18 Ω. What is its cross-section in mm²? (ρ = 0.4 Ω·mm²/m)
0.2
3
Wire A: 4 m, 1 mm²; wire B: 2 m, 0.5 mm² (same material). Compare their resistances.
They are equal: R_A = 4ρ, R_B = 2ρ : 0.5 = 4ρ.
4
Name three everyday devices that use a potentiometer.
The volume knob of a radio or TV, a lamp dimmer, a music system.
5
Two wires of the same metal and length have cross-sections of 1 mm² and 0.25 mm². Which has the larger resistance, and how many times larger?
The thin (0.25 mm²) wire has 4 times the resistance, because R is inversely proportional to S.