Ohm’s law
Answers are for parents and teachers.
1
A resistor R = 25 Ω carries 0.8 A. What is U in volts?
20
2
A lamp draws 0.3 A at 6 V. What is its resistance in ohms?
20
3
A copper wire (ρ = 0.017 Ω·mm²/m), l = 200 m, S = 0.85 mm². What current flows at 2 V?
R = 0.017 · 200 : 0.85 = 4 Ω; I = 2 : 4 = 0.5 A.
4
If the voltage is constant and the resistance becomes 3 times larger, how does the current change?
It becomes 3 times smaller.
5
A lamp is marked “2.5 V; 0.3 A”. What does this tell us? Find R.
The lamp draws 0.3 A at 2.5 V; R = 2.5 : 0.3 ≈ 8.3 Ω.