Draw the electric field lines around a positive charge.Calculate the electric force that exists between two objects that are 0.500 m apart and carry charges of 0.00450 C and 0.00240 C. Is this force attractive or repulsive?

Question 1: Electrostatics (11 points)

a. Draw the electric field lines around a positive charge. (2 points)

b. Calculate the electric force that exists between two objects that are 0.500 m apart and carry charges of 0.00450 C and 0.00240 C. Is this force attractive or repulsive? (3 points)

c. How does the size of the electric force between two charged objects change if the amount of charge on one of the objects is doubled? (2 points)

d. How does the size of the electric force between two charged objects change if the charges are moved farther apart? (1 point)

Question 2: Energy and Capacitance (6 points)

a. Calculate the electric potential energy stored in a capacitor that stores 3.40 × 10–10 C of charge at 20.0 V. (2 points)

 

b. Two negative charges are moved closer together. Write one or two sentences to describe the energy conversion that happens. (2 points)

 

 

 

 

 

c. Calculate the capacitance of a system that stores 4.0 × 10–10 C of charge at 25.0 V. (2 points)

 

Question 3: Current and Resistance (7 points)

a. Write two or three sentences to describe the conductivity of a conductor. Explain its conductivity in terms of the electrons in it. (2 points)

 

b. What is resistance? How does the resistance of a long wire compare with the resistance of a short wire? How does the resistance of a thick wire that has a large cross-sectional area compare with the resistance of a thin wire? (3 points)

 

 

 

c. What is the power of a lightbulb that has a current of 0.480 A at 120.0 V? (2 points)

 

Question 4: Circuits (13 points)

a. In the circuit below, identify how the resistors are connected and then identify the quantity that must always be the same for these resistors. (2 points)

 

 

b. Write two or three sentences to describe what a voltmeter measures about a resistor and how it should be connected with the resistor in a circuit. (2 points)

 

 

c. What is the voltage drop across a 40.0 Ω resistor that has a 0.350 A current? (2 points)

 

 

 

d. In the space below, draw and label a circuit diagram that has a 24.0 V power supply and two 10.0 Ω resistors connected in parallel. (2 points)

 

 

e. What is the equivalent resistance of a 3.0 Ω resistor and a 6.0 Ω resistor connected in parallel? (2 points)

 

 

f. Describe how a fuse works to prevent dangerous currents in some circuits.

 

 

g. In the circuit below, identify all resistors that will stop working when the switch is opened. (1 point)

 

Question 5: Magnetism (4 points)

a. Draw the magnetic field lines between the two ends of the magnets and describe whether the magnetic force between the magnets is attractive or repulsive. (2 points)

 

 

b. A small bar magnet is oriented to the magnetic field shown. Write N and S on the small bar magnet to show how its poles would be oriented in the magnetic field. (2 points)

Question 6: Electromagnetism (9 points)

a. How does using more loops of wire in an electromagnet affect the strength of the magnetic field? (2 points)

 

 

 

b. Write two or three sentences to identify the energy conversion that takes place in an electric motor and to describe how electromagnetism is involved. (2 points)

 

 

c. What does a step-down transformer change in an alternating current? (2 points)

 

d. What is the magnetic force on a particle that has 0.000500 C of charge and is moving at 2.50 × 105 m/s to the right through a magnetic field that is 4.20 T and pointing away from you? Specify both magnitude and direction in your answer. (3 points)

 

 

 

 

 

 

 

 

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