Download If the current flowing in a wire is 1 milliamp (0

1.
The electric field of a capacitor is 8000 N/C and the voltage across the capacitor is 400 V. (a) What is the separation of the plates? (b) What
is the electric potential energy of an electron being held at the negative plate?
0.05 m
6.4 E –17 J
2. The electric field between in a capacitor is 8000 N/C and the plates are 5 cm (5 E –2 m) apart. (a) What is the voltage across the plates? (b)
What force is acting on a proton when it is in between the plates? (c) What work would be done to move the proton from the negative to the
positive plate of the capacitor?
400 V
1.28 E –15 N
6.4 E –17 J
3. A voltmeter reads 400 V across a capacitor and the plates are 0.05 m apart. (a) What is the electric field between the plates? What are the
(b) force and (c) acceleration of a proton (m = 1.67 E –27 kg) in this electric field? (d) If the proton started from rest at the positive plate
and traveled to the negative plate (which is a distance of 0.05 m away – the plate separation), what is its final velocity? (e) What is the
kinetic energy of the proton when it reaches its final velocity?
8000 N/C
1.28 E –15 N
7.66 E 11 m/s2
276851 or 2.77 E 5 m/s
6.4 E –17 J
4. The current flowing in a wire is 1 milliamp (0.001 A). Find (a) the charge passing a given point in 1 second and (b) the number of electrons
passing a given point in 1 second.
0.001 C
6.25 E 15 electrons
5. The current through a toaster connected to 120 V is 8 A. What is the resistance of the toaster?
15 , Also in case you care P of the toaster is 960 W, The energy used in the toaster in 45 seconds is 43,200 J, and the charge passing by in 45
seconds 360 C.
6. A 4000-W clothes dryer is connected to a 220-V circuit. How much current does the dryer draw?
18.2 A
7. A 75-W bulb is plugged into 120-V circuit. (a) What is the current flowing through the bulb? (b) What is the resistance of the bulb?
0.625 A
192
8. A 120-V circuit is connected to a light bulb and 0.333 A of current flow through the bulb. (a) What is the resistance of the bulb? (b) What
is the power of the bulb? (c) If the bulb is on for 3600 seconds, what energy is used by the bulb? (d) Knowing what you do about light
bulbs, guess what kind of energy other than light most of this energy is converted to.
360  40W
144,000 J
Heat
9. A 6.0-V battery delivers a 0.50-A current to an electric motor across its terminals. Find (a) the resistance of the motor, (b) the power
consumed by the mower and (c) if the motor runs for 5.0 minutes, how much electric energy is delivered?
12
3W
900 J
10. Look at your answers to 1 (b), 2 (c), and 3 (e) from this homework. Notice that each capacitor and has the same separation of plates,
voltage, and electric field to start with. Notice that 1 (b), 2 (c), and 3 (e) each asked you to calculate a different type of energy for the
capacitor. What is the big AHA! I want you to get from this? Think about this AND USE YOUR NEWLY GAINED KNOWLEDGE to
make sure the first three parts of the next homework question are EASY to answer.
The Big Aha:
Hey all the energies are the same!! Hey energy must be conserved. That must be why Ms. Walker wrote all the equations
involved in electrical energy to be equal to each other and so on the equation sheet it looks like this: UE = qV = W = Fd = ½ mv2
11. A capacitor is charged up to 60.0 V and the separation between the plates of the capacitor is 3.0 cm (3 E-2 m) apart. (a) What is the electric
potential energy of a proton held at the positive plate of this capacitor? (b) What is work would be done to move a proton from the negative
plate of the capacitor to the positive plate? (c) If a proton is held at the positive plate of the capacitor and then released, what would be its
final kinetic energy as it hit the negative plate? (d) Would this answer be any different if I had substituted the word electron in (a) and (b)
and (c) and changed the words positive to negative and vice versa? (e) Your conclusion to (d) should be that the answers would all be the
same for an electron because it has the same charge as a proton. HOWEVER, the mass of a proton is 1.67 E –27 kg and the mass of an
electron is 9.11 E –31 kg. The mass of the electron is much, much smaller. Now, qualitatively (no numbers) answer this next question. (f)
Even though the electron and the proton would have the same energy, how would their acceleration and the final velocities be different in
the capacitor given their significant difference in mass?
9.6 E –18 J
9.6 E –18 J
9.6 E –18 J AND YOU SHOULD HAVE MADE ONLY ONE CALCULATION!
No different for an electron because its charge is the same as a protons
(e) requires no answer
(f) The acceleration of the much lighter electron should be about 1000 times higher and its velocity will be significantly higher also about 30
times higher.