A wire of resistance 4 Ω is used to wind a single-layer circular coil of radius 7 cm. The wire has a diameter of 1.4 mm and the specific resistivity of its material is 2 × 10-7 Ω m. Find the total number of turns in the coil.

A room heater is rated 400 W, 220 V. If the supply voltage drops to 200 V, what will be the power consumed (approximately)?

A resistor is connected to a battery of 12 V emf and internal resistance 2 Ω. If the current in the circuit is 0.6 A, the terminal voltage of the battery is: