Question

To practice Problem-Solving Strategy 25.1 Power and Energy in Circuits. A device for heating a cup of water in a car connects to the car's battery, which has an emf E = 10.0 V and an internal resistance rint = 0.03 Ω . The heating element that is immersed in the cup of water is a resistive coil with resistance R. David wants to experiment with the device, so he connects an ammeter into the circuit and measures 10.0 A when the device is connected to the car's battery. From this, he calculates the time to boil a cup of water using the device. If the energy required is 100 kJ , how long does it take to boil a cup of water?

Answer 1

Answer:

 t = 1030 s

Explanation:

Let's start by calculating the resistance of the coil,

    V = I (R + ri)

    R = V / I - ri

    R = 10/10 -0.03

    R = 0.97  Ω

Now we can calculate the power supplied to the water

   P = I2 R

   P = 10 2 0.97

   P = 97 w

Work energy is power for time

   E = W = P t

   t = W / P

   t = 100 103/97

   t = 1030 s