15.) The joule heating in a wire with resistance of 5 ohms amounts to 500 watts. How much current flows through this wire?

a) 10 amps b) 15 amps c) 45 amps d) 75 amps e) 100 amps

23. When the early Universe was cooling down if a photon has a wavelength of 1.44 x 10-17 m, how much energy did that photon have?

a) 1.38 x 10-8 joules b) 4.14 x 10-8 joules c) 5.5 x 10-10 joules d) 8.5 x 10-12 joules e) 3 x 10-15 joules

26. Ten watts of visible light shining on a solar cell produce just enough electricity to light 5 LED bulbs. Each LED bulb is 0.5 watts. What is the efficiency of this process?

a) 0.5% b) 2.5% c) 5.0% d) 25% e) 75%

27. You want to use a solar panel to generate enough power to light one 18-watt compact fluorescent bulb. Your solar panel measures 50 cm by 80 cm. The average value of the summer solar insolation of your location is 150 watts/m2. How efficient must your solar panel be to produce the power needed?

a) 15% b) 18% c) 30% d) 35% e) 45%