Download Homework Problems

Pre AP Physics
Electric Circuits and Magnetism WS
1. Four 15 Ώ resistors are connected in series with a 45 V battery, what is the current in the circuit? [0.75 A]
2. There are three 30 Ώ resistors connected in series across a 120 V generator.
a. What is the equivalent resistance of the circuit? [90 Ώ]
b. What is the current in the circuit? [1.333 A]
3. A 10 Ώ resistor, a 15 Ώ resistor and a 5 Ώ resistor are connected in series across a 90 V battery.
a. What is the equivalent resistance of the circuit? [30 Ώ]
b. What is the current in the circuit? [3 A]
4. Ten Christmas tree bulbs connected in series have equal resistances. When connected to a 120 V outlet, the current
through the bulbs is 0.06 A.
a. What is the equivalent resistance of the circuit? [2000 Ώ]
b. What is the resistance of each bulb? [200 Ώ]
5. A 9.0 V battery is connected to four light bulbs in series, one light bulb has a resistance of 2.0 Ώ, another has a resistance
of 4.0 Ώ, the third has a resistance of 5.0 Ώ and the fourth has a resistance of 7.0 Ώ.
a. Find the equivalent resistance for the circuit. [18Ω]
b. Find the current in the circuit. [0.5 A]
c. The current found in part b must be the current in each resistor in the circuit. Find the potential difference across each
resistor. [1V, 2V, 2.5 V, 3.5 V]
6. A 7.0 Ώ resistor is connected in series with another resistor and a 4.5 V battery. The current in the circuit is 0.60 A.
Calculate the value of the unknown resistance. [0.5 Ώ]
7. Several light bulbs are connected in series across a 115 V source of emf.
a. What is the equivalent resistance if the current in the circuit is 1.70 A? [67.647 Ώ]
b. If each light bulb has a resistance of 1.50 Ώ, how many light bulbs are in the circuit? [45 bulbs]
8. Three resistors of 60 Ώ, 30 Ώ and 20 Ώ are connected in parallel across a 90 V difference in potential.
a. Find the equivalent resistance of the circuit. [10Ω]
b. Find the current in the entire circuit. [9 A]
c. Find the current through each branch of the circuit. [1.5A, 3 A, 4.5 A]
9. Three 15 Ώ resistors are connected in parallel and placed across a 30 V potential difference.
a. Find the equivalent resistance of the circuit. [5 Ώ]
b. Find the current in the entire circuit. [6 A]
c. Find the current through each branch of the circuit. [2A, 2A, 2A]
10. A 12.0 Ώ resistor and a 15 Ώ resistor are connected in parallel and placed across the terminal of a 15 V battery.
a. Find the equivalent resistance of the circuit. [6.670 Ώ]
b. Find the current in the entire circuit. [2.249 A]
c. Find the current through each branch of the circuit. [1.25 A, 1 A]
11. Suppose the 12 Ώ resistor in problem #10 is replaced by a 10 Ώ resistor.
a. Does the equivalent resistance become smaller, larger, or remain the same? What is the new resistance? [5.988Ω]
b. Does the amount of current through the entire circuit change? In what way? [2.505 A]
c. Does the amount of current through the 15 Ώ resistor change? In what way? [1A]
12. An 18 Ώ, 9.00 Ώ and 6.00 Ώ resistor are connected in parallel to an emf source. A current of 4.00 A is in the 9.00 Ώ
resistor.
a. Calculate the equivalent resistance of the circuit. [3.003Ω]
b. What is the potential difference across the source? [36 V]
c. Calculate the current in the other resistors. [2A, 6A]
13. For each of the following sets of values, determine the equivalent resistance for the circuit shown in the figure below.
a. Ra = 25.0 Ώ
b. Ra = 12.0 Ώ
Rb = 3.0 Ώ
Rb = 35.0 Ώ
Rc = 40.0 Ώ
Rc = 25.0 Ώ
[27.791 Ώ]
[26.583 Ώ]
14. For the following set of values, determine the equivalent resistance for the circuit shown in the figure below.
a. Ra = 25.0 Ώ
[50.861 Ώ]
Rb = 3.0 Ώ
Rc = 40.0 Ώ
Rd = 15.0 Ώ
15. For the following circuit find:
a. the equivalent resistance [6.6 Ώ]
b. the total current [1.818 A]
c. the current and potential difference in the 3 Ώ resistor [1.818 A, 5.454 V]
d. the current and potential difference in the 6 Ώ resistor [1.091 A, 6.545 V]
e. the current and potential difference in the 9 Ώ resistor [0.727 A, 6.545 V]
16. For the following circuit find:
a. the equivalent resistance [9.833 Ώ]
b. the current and the potential difference in the 1.5 Ώ resistor [1.831 A, 2.747 V]
17. For the following circuit find:
a. the equivalent resistance [13.167 Ώ]
b. the current in and the potential difference across the 1.5 Ώ resistor [0.911 A, 1.367 V]
Re = 18.0 Ώ
18. A proton, with a charge of 1.6 x 10-19 C, moving east experiences a force of 8.8 x 10-19 N upward due to the Earth’s
magnetic field. At this location, the field has a magnitude of 5.5 x 10-5 T to the north. Find the speed of the particle. [1.0 x 10 5
m/s]
19. A proton, with a charge of 1.6 x 10-19 C, moves perpendicularly to a magnetic field that has a magnitude of 4.20 x 10 -2 T.
What is the speed of the particle if the magnitude of the magnetic force on it is 2.40 x 10 -14 N? [3.571 x 106m/s]
20. A proton, with a charge of 1.6 x 10-19 C, traveling to the right along the x-axis (east) enters a region where there is a
magnetic field of magnitude 2.5 T directed upward along the y-axis (north). If the proton experiences a force of 3.2 x 10-12 N,
find the speed of the proton. [8.0 x 106m/s]
21. If an electron, with a charge of 1.6 x 10-19 C, in an electron beam experiences a downward force of 2.0 x 10 -14 N while
traveling in a magnetic field of 8.3 x 10-2 T west, what is the direction and magnitude of the velocity? [1.51 x 10 6m/s, north]
22. A uniform 1.5 T magnetic field points north. If an electron, with a charge of 1.6 x 10 -19 C, moves vertically downward
(toward the ground) with a speed of 2.5 x 107 m/s through this field, what force (magnitude and direction) will act on it? [6.0 x
10-12 N, west]
23. A proton, with a charge of 1.6 x 10-19 C, moves straight upward (away from the ground) through a uniform magnetic field
that points from east to west and has a magnitude of 2.5 T. If the proton moves with a speed of 1.5 x 10 7 m/s through this
field, what force (magnitude and direction) will act on it? [6.0 x 10 -12 N, south]
24. An alpha particle (the nucleus of a helium atom, carrying a charge of 3.2 x 10-19 C) moves at 5.5 x 107 m/s at a right
angle to a magnetic field. If the particle experiences a force of 1.5 x 10 -14 N due to the magnetic field, when what is the
magnitude of the magnetic field? [8.52 x 10-4 T]
25. A wire 36 m long carries a current of 22 A from east to west. If the maximum magnetic force on the wire at this point is
downward (toward Earth) and has a magnitude of 4.0 x 10 -2 N, find the magnitude and direction of the magnetic field at this
location. [5.05 x 10-5 T, south to north]
26. A 6.0 m wire carries a current of 7.0 A toward the east. A magnetic force of 7.0 x 10 -6 N acts on the wire upwards. Find
the magnitude and direction of the magnetic field producing the force. [1.67 x 10 -7 T, north]
27. A wire 1.0 m long experiences a magnetic force of 0.50 N due to a perpendicular uniform magnetic field. If the wire
carries a current of 10.0 A, what is the magnitude of the magnetic field? [0.050 T]
28. The magnetic force on a straight 0.15 m segment of wire carrying a current of 4.5 A is 1.0 N. What is the magnitude of
the component of the magnetic field that is perpendicular to the wire? [1.48 T]
29. The magnetic force acting on a wire that is perpendicular to a 1.5 T uniform magnetic field is 4.4 N. If the current in the
wire is 5.0 A, what is the length of the wire that is inside the magnetic field? [0.59 m]
30. A particle with a charge of 0.030 C experiences a magnetic force of 1.5 N while moving at right angles to a uniform
magnetic field. If the speed of the charge is 620 m/s, what is the magnitude of the magnetic field the particle passes
through? [0.081 T]
31. An electron moving north encounters a uniform magnetic field. If the magnetic field points east, what is the direction of
the magnetic force on the electron? Explain. [upward]
32. A straight segment of wire has a length of 25 cm and carries a current of 5.0 A. If the wire is perpendicular to a magnetic
field of 0.60 T, then what is the magnitude of the magnetic force on this segment of the wire? [0.75 N]
33. Two parallel wires have charges moving in the same direction. Is the force between them attractive or repulsive?