# Describe the direction of the electric force between two opposite charges, between two like charges, and when a charge is in an electric field.

### Physics Electricity and Magnetism

Question 1 (4 points)

1. Make a drawing of the electric field lines around a positive charge, then make a second drawing of the electric field lines around a negative charge. (1 point)
2. What is the mathematical equation for the electric force between two charges? Identify each variable. (1 point)
3. Describe the direction of the electric force between two opposite charges, between two like charges, and when a charge is in an electric field. (1 point)
4. A metal sphere is neutral because it has an equal number of protons and electrons. Draw how the charges in the sphere are redistributed when a negatively charged rod is brought near it. (1 point)

Question 2 (3 points)

a. Describe how electric potential energy, kinetic energy, and work change when two charges of opposite sign are placed near each other. (1 point)

1. Complete the table to show the effect of each change on each electric quantity. (1 point)
 Change Effect on electric force Effect on electric potential energy Effect on potential difference Multiply one charge by 2 Multiply distance by 2
1. What is the mathematical equation for capacitance? Identify each variable. (1 point)

Question 3 (4 points)

a. What is the mathematical equation for Ohm’s law? Identify each variable. (1 point)

2. What is the potential difference across a 15 Ω resistor that has a current of 3.0 A? (1 point)
3. Review quantities associated with electric circuits by completing the table. (1 point)
 Symbol Units (full name and abbreviation) Potential difference Current Resistance Capacitance Charge
1. Fill in the blanks in the following paragraph to correctly identify the conductive properties of materials. (1 point)

A metal such as copper is a(n) _______________ because it provides a pathway for electric charges to move easily. A material such as rubber is a(n) _______________ because it _______________ the flow of electric charges. A material that partially conducts electric current is a(n) _______________. These materials include _______________ elements.

Question 4 (3 points)

a. Review the properties of meters used in electric circuits by placing an X in the correct column. (1 point)

 Ammeter Voltmeter Measures current Measures potential difference Connected in parallel Connected in series Measurement expressed in amperes Measurement expressed in volts Measures the amount of charge per second passing through Measures the change in energy per unit charge between two points
1. Write a few sentences comparing three different kinds of circuits: complete, open, and short circuits.
2. Describe how fuses and circuit breakers protect against electrocution and household fires. How do you restore a broken circuit after the problem has been corrected? (1 point)

Question 5 (4 points)

a. Examine the lightbulbs in the circuit below. Write a sentence explaining what would happen if lightbulb A burned out. Repeat this for lightbulbs B, C, and D. (1 point)

1. What is the equivalent resistance if you connect three 10.0 Ω resistors in series? (1 point)
2. What is the equivalent resistance if you connect three 10.0 Ω resistors in parallel? (1 point)
3. Calculate the current in each 10.0 Ω resistor in the series circuit and in the parallel circuit if the power supply is 60.0 V. (1 point)

Question 6 (3 points)

a. What are the ends of a magnet called? Describe the forces that occur when two magnets are brought close together. (1 point)

1. Draw a bar magnet, label its poles, and draw the magnetic field lines around it. (1 point)
2. Explain what happens when you cut a magnet in half. (1 point)

Question 7 (4 points)

a. Compare permanent magnetism, induced magnetism, and electromagnetism. (1 point)

3. Fill in the blanks in the following paragraph to correctly identify the properties of devices that use electromagnetism. (1 point)

A(n) ____________________ changes mechanical energy into ____________________. A(n) ____________________ changes electric energy into ____________________. A(n) ____________________ changes the voltage of an alternating current. A(n) ____________________ transformer has more loops in the primary coil than in the secondary coil. A(n) ____________________ transformer has ____________________ loops in the primary coil than in the secondary coil.

4. Describe how to use right-hand rules to relate the directions of magnetic fields, currents, moving charges, and forces. (1 point)
5. What is the mathematical equation for calculating the force on a charged particle moving through a magnetic field? Identify each variable. (1 point) 