5 A pet shop owner has a glass tank with an open top measuring 50.0 cm x 120.0 cm. The owner wants to illuminate the plants inside with light of 10 W and wants to know what wattage bulb to use in the light fitting 60.0 cm directly above the tank. Determine the value. 6 Assume the helium-neon lasers commonly used in student physics laboratories have power outputs of 0.50 mW. a A laser beam is projected onto a circular spot 1.00 mm in diameter. Calculate the intensity of I the light at the spot. b An intensity of 100 W cm 2 is required to set fire to paper. Deduce how a laser beam could be made small enough to achieve this.5 A pet shop owner has a glass tank with an open top measuring 50.0 cm x 120.0 cm. The owner wants to illuminate the plants inside with light of 10 W and wants to know what wattage bulb to use in the light fitting 60.0 cm directly above the tank. Determine the value. 6 Assume the helium-neon lasers commonly used in student physics laboratories have power outputs of 0.50 mW. a A laser beam is projected onto a circular spot 1.00 mm in diameter. Calculate the intensity of I the light at the spot. b An intensity of 100 W cm 2 is required to set fire to paper. Deduce how a laser beam could be made small enough to achieve this