Physics for Friday, April 23 @ HSAS

3. A current of 0.20 A is kept flowing in a wire by a
10-V battery for 5.0 s. (a) What power is
supplied to the wire? (b) How much electrical
energy has been delivered to the wire?
𝑃 = 𝑉𝐼
𝑃 = (10 𝑉)(0.20 𝐴)
𝑃 = 2 𝑤𝑎𝑡𝑡𝑠
𝑊 = 𝑃𝑡
𝑊 = (2 𝑤𝑎𝑡𝑡𝑠)(5.0 𝑠)
𝑊 = 10 𝐽𝑜𝑢𝑙𝑒𝑠

5. A 110-V motor draws 0.50 A of current. (a) What
power is being supplied to the motor? (b) How
much work does this motor do in 10 seconds?
𝑃 = 𝑉𝐼
𝑃 = (110 𝑉)(0.50 𝐴)
𝑃 = 55 𝑤𝑎𝑡𝑡𝑠
𝑊 = 𝑃𝑡
𝑊 = (55 𝑤𝑎𝑡𝑡𝑠)(10 𝑠)
𝑊 = 550 𝐽𝑜𝑢𝑙𝑒𝑠

7. A 200-V generator powers an electric heater.
(a) How much work is done on each coulomb of
charge moved through the heater?
(b) How much work in joules is done on each
electron moved through the heater?
𝑊 = 𝑞𝑉 = (1𝐶)(200𝑉) = 200 𝐽𝑜𝑢𝑙𝑒𝑠
𝑊 = 𝑞𝑉 = (1.60 × 10−19
𝐶)(200 𝑉)
= 3.2 × 10−17
𝐽𝑜𝑢𝑙𝑒𝑠

9. A 60-W lamp is operating on a 120-V line.
(a) How much current passes through the lamp?
(b) How many electrons pass through the lamp in
4.0 s?
𝑃 = 𝑉𝐼
60 𝑤𝑎𝑡𝑡𝑠 = (120 𝑉) ∙ 𝐼
𝐼 = 0.5 𝐴

10. A 60-W lamp is operating on a 120-V line.
(a) How much current passes through the lamp?
(b) How many electrons pass through the lamp in
4.0 s?
𝐼 = 0.5 𝐴
𝐼 =
∆𝑞
𝑡
0.5 𝐴 =
∆𝑞
4.0 𝑠
∆𝑞 = 2𝐶
2𝐶/(1.60 × 10−19
𝐶) = 1.25 × 1019
𝑒

13. A stereo plugged into a 120-volt outlet draws 0.1 A of
current.
a. How much charge goes into the stereo each second?
b. How much power does the stereo use?
c. How much energy does the stereo use up in 1
minute?

15. A 240-Ω lamp is connected to a 120-volt outlet.
a. How much power does it dissipate?
b. How much current does it draw?