well i am sure you need this to so look really hard at this then delete it
Explanation:
1. The speed with which electrons move through a copper wire is typically 10-4 m s-1
.
a. Explain why is it that the electrons cannot travel faster in the conductor?
b. Explain why the electron drift produces heat?
1. a) collisons with the crystal lattice atoms b) collisions with lattice atoms transfers energy.
2. Explain in terms of atomic and electron movement, why resistance increases with temperature.
2. Electrons drift through the lattice, as temperature increases the lattice atoms vibrate more and this increases the probability of
collision and hence resistance to electrons has increased.
3. Calculate the resistance of an aluminum (ρ = 2.8x10-8 Ωm) wire that is 2.0 m long and of circular cross section
with a diameter of 1.5 mm.
3. 32 mΩ
4. Determine the length of tungsten (ρ = 5.6x10-8 Ωm) wire with a diameter of 1.0 mm that is used to make a 20.0 Ω resistor.
4. 280 m
5. A nichrome (ρ = 100x10-8 Ωm) wire has a diameter of 0.40 mm. Calculate the length of this wire needed to carry a current
of 30 mA when there is a potential difference of 12 V across it.
5. 50 m
6. A thin copper (ρ = 1.68x10-8 Ωm, but you don’t need it) wire 200 cm in length has a 9 V dry cell connected between its ends.
Determine the voltage drop that occurs along 30 cm of this wire.
6. 1.35 V
7. If the potential difference across the bulb in a camping lantern is 9.0 V, what is the potential difference across the battery used to
power it?
battery gives the voltage of 9.0 V to the lantern to use it.
8. How much current, in amperes, is in a lightning stroke that lasts 0.05 second and transfers 100 coulombs?
I = q/t = (100 C)/(0.05 s) =2000 A
9. Calculate the resistance of the filament in a light bulb that carries 0.4 A when 3.0 V is impressed across it.
V = IR R = V/I = 7.5 Ω
10. Electric socks, popular in cold weather, have a 90-ohm heating element that is powered by a 9-volt battery.
How much current warms your feet?
V = I/R = 0.1 A
11. Calculate the current of a lightning bolt that delivers a charge of 35 coulombs to the ground in a time of 1/1000 second.
11. I = q/t = 35 000 A.
12. Calculate the current where 10 coulombs of charge pass a point in 5 seconds.
12. I = V/R = 2 A
13. Two light bulbs designed for 120-V use are rated at 40W and 60W. Which light bulb has the greater filament resistance? Why?
13. More current flows in the 60-W bulb, which means the resistance of the filament is less.
P = IV = V2/R, R = V2/P = (120 V)2/(60 W) = 240 Ω; for the 40-W lamp, R = (120 V)2/(40 W) = 360 Ω
14. A battery does 18 joules of work on 3 coulombs of charge. What voltage does it supply?
14. V= E/q= (18 J)/(3 C) = 6V
15. A power line with a resistance of 2 ohms has a current of 80 A in it. The power dissipated in the line is
15. 12800 W.
2
16. A toaster oven is plugged into an outlet that provides a voltage difference of 120 V.
What power does the oven use if the current is 10A?
16. P = IV = 1200 W
17. A VCR that is not playing still uses 10.0 W of power. What is the current if the VCR is plugged into a 120 V electric outlet? 17.
17. P = IV I = P/V = 0.083 A
18. A flashlight bulb uses 2.4 W of power when the current in the bulb is 0.8 A. What is the voltage difference?
18. P = IV V = P/I = 3V
19. A refrigerator operates on average for 10.0 h a day. If the power rating of the refrigerator is 700 W, how much electrical energy
does the refrigerator use in 1 day? (make sure to convert to kW)
19. E = Pt = (0.7 kW)(10.0 h) = 7 kWhours
20. A TV with a power rating of 200 W uses 0.8 kWh in one day. For how many hours was the TV on during this day?
20. E = Pt t = E/P= 0.8 kWh/0.2 kW = 4 h
21. Calculate the voltage difference in a circuit with a resistance of 25 Ω if the current in the circuit is 0.5 A.
21. V = IR = 12.5 V
22. A current of 0.5 A flows in a 60 W light bulb when the voltage difference between the ends of the filament is 120 V.
What is the resistance of the filament?
22. R = V/I = 240 Ω
23. A toy car with a resistance of 20 Ω is connected to a 3 V battery. How much current flows in the car?
23. I = V/R = 0.15 A
24. The current flowing in an appliance connected to a 120 V source is 2 A. How many kilowatt-hours of electrical energy does the
appliance use in 4 h? (2 equations used & convert watts to kW)
24. E = Pt P = IV = 0.24 kW E = 0.96 kWh
25. A calculator uses 9 V battery & draws 0.1 A of current. How much power does it use?
25. P = IV = 0.9 W
26. A battery causes 250 mA to flow when it is applied to a light bulb with a resistance of 50 ohms. How much current would flow if
the same source were applied to a 12 ohm resistor?
26. voltage of the source: V = IR = 12.5 V I = V/R = 1.04 A
