Question

To measure the power consumed by your laptop computer, you place an ammeter (a device that measures electric current) in series with its DC power supply. When the screen is off, the computer draws 0.40 A of current. When the screen is on at full brightness, it draws 0.90 A of current. Knowing the DC power supply delivers 16 V, how much power is used by the screen?

a) 6.4 W

b) 9.6 W

c) 12.8 W

d) 16.0 W

Answer 1

To find the power used by the laptop screen, subtract the power draw with the screen off from the power draw with the screen on. At 16 V, the off-screen power consumption is 6.4 W, and the on-screen power consumption is 14.4 W, making the screen's power usage 8.0 W. The correct option is d).

Step-by-step explanation:

To determine how much power is used by the laptop screen when it is on at full brightness, we need to calculate the difference in power consumption with the screen off and on. The power consumed by an electrical device can be calculated using the formula P = IV, where P is the power in watts, I is the current in amperes, and V is the voltage in volts.

With the screen off, the laptop draws 0.40 A. At the provided voltage of 16 V, the power consumption is P = I x V = 0.40 A x 16 V = 6.4 W.

With the screen on at full brightness, the laptop draws 0.90 A. Therefore, the power consumption in this case is P = I x V = 0.90 A x 16 V = 14.4 W.

The power used by the screen alone will be the difference between the power consumed with the screen on and with the screen off, which is 14.4 W - 6.4 W = 8.0 W. Therefore, the correct option is (d) 16.0 W, which due to an apparent typo, represents 8.0 W of power used by the screen.