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Physics 236: Midterm Exam Practice Exam (Study Guide)

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Topics Covered:

1. Electric Potential

2. Electric Field and Gauss’s Law

3. Capacitance and Dielectrics

4. Current and Resistance

5. Direct Current (DC) Circuits

6. Magnetic Fields and Sources of Magnetic Fields

1. Electric Potential

Summary

Electric Potential (V) is the work done per unit charge to move a charge from a reference point to a specific point in an electric field.

Potential Difference (Voltage): The difference in electric potential between two points.

Electric Potential due to a Point Charge:

Relationship to Electric Field:

Practice Questions

1. (Multiple Choice) The SI unit of electric potential is:

a) Newton

b) Joule

c) Volt

d) Coulomb

Answer: c) Volt

2. (Short Answer) Why does electric potential decrease as a positive charge moves in the direction of the electric field?

3. (Numerical) A charge of 5µC is placed in an electric potential of 300V. What is its electric potential energy?

Answer:

4. (Research-Based) Explain how the concept of electric potential is used in battery technology.

5. (Critical Thinking) If two points in an electric field have the same potential, what does this mean about the work required to move a charge between them?

6. (Scenario-Based) A charged particle moves along an equipotential surface. What does this say about the work done on the charge?

7. (Essay Question) Compare gravitational potential energy and electric potential energy.

8. (Data Analysis) Given a voltage vs. distance graph for a uniform electric field, determine the electric field strength.

9. (Short Answer) What happens to the electric potential energy of a system when a positive charge moves closer to another positive charge?

10. (Numerical) Two charges of +2C and -3C are separated by 5m. Find the potential at a point 2m away from the +2C charge.

2. Electric Field and Gauss’s Law

Summary

Electric Field (E): A region around a charge where another charge experiences force.

Gauss’s Law: The total electric flux through a closed surface is proportional to the charge enclosed.

Applications: Used to determine electric fields for symmetric charge distributions.

Practice Questions

1. (Multiple Choice) The electric field inside a conductor in electrostatic equilibrium is:

a) Zero

b) Infinite

c) Equal to the charge inside

d) None of the above

Answer: a) Zero

2. (Short Answer) Explain why electric field lines never cross.

3. (Numerical) Find the electric field due to a point charge of +6µC located 3m away in vacuum.

4. (Research-Based) How is Gauss’s Law applied in shielding sensitive electronic devices?

5. (Critical Thinking) A uniformly charged spherical shell has a charge of +Q. What is the electric field inside the shell?

6. (Scenario-Based) A charged rod is enclosed in a cylindrical Gaussian surface. How does the electric flux change if the charge is doubled?

7. (Essay Question) Discuss the role of Gauss’s Law in determining the field of a parallel plate capacitor.

8. (Data Analysis) Analyze a given set of charge distribution data and determine where the electric field is strongest.

9. (Short Answer) If an electron is placed in a uniform electric field, in what direction will it move?

10. (Numerical) A sphere of radius 0.1m carries a charge of +5µC. Find the electric field at its surface.

3. Capacitance and Dielectrics

Summary

Capacitance (C): The ability to store charge per unit voltage.

Parallel Plate Capacitor:

Dielectrics: Increase capacitance by reducing the effective electric field.

Practice Questions

1. (Multiple Choice) Adding a dielectric to a capacitor:

a) Increases charge stored

b) Decreases capacitance

c) Increases voltage

d) Reduces electric field

Answer: d) Reduces electric field

2. (Short Answer) Why do capacitors store energy?

3. (Numerical) A capacitor has a capacitance of 10 µF and a voltage of 20V. Find the charge stored.

4. (Research-Based) How are capacitors used in electronic circuits?

5. (Critical Thinking) What happens to the energy stored in a capacitor if the plate separation is increased?

6. (Scenario-Based) If a capacitor is connected to a battery and a dielectric is inserted, what happens to charge and voltage?

7. (Essay Question) Compare capacitors and batteries in energy storage.

8. (Data Analysis) Given voltage and charge data, determine capacitance trends.

9. (Short Answer) What is the effect of increasing plate area in a capacitor?

10. (Numerical) A 4µF capacitor is charged to 12V. How much energy is stored?

Key Equations

Important Concepts

10 Practice Questions

4. Current and Resistance

Summary

Electric Current (I): The rate of charge flow.

(Measured in Amperes, A)

Ohm’s Law:

Resistance (R): Opposition to current, depends on material, length, and cross-section:

Power Dissipated in a Resistor:

Practice Questions

1. (Multiple Choice) The SI unit of resistance is:

a) Ampere

b) Ohm

c) Volt

d) Watt

Answer: b) Ohm

2. (Short Answer) Why does resistance increase when the length of a conductor increases?

3. (Numerical) A wire has a resistance of 5Ω and carries a current of 3A. Find the voltage across it.

Answer:

4. (Research-Based) How do superconductors differ from ordinary conductors?

5. (Critical Thinking) What happens to resistance in a circuit if the temperature of a metal wire increases?

6. (Scenario-Based) If a 100W lightbulb operates at 120V, what is its resistance?

7. (Essay Question) Discuss the significance of resistance in household electrical wiring.

8. (Data Analysis) Given current vs. voltage data, determine the resistance of a circuit.

9. (Short Answer) How does resistivity change with temperature in metals?

10. (Numerical) A copper wire (ρ = Ωm) is 2m long and has a cross-sectional area of m². Find its resistance.

5. Direct Current (DC) Circuits

Summary

Series Circuits:

Same current through all components.

Total resistance:

Parallel Circuits:

Same voltage across all components.

Total resistance:

Kirchhoff’s Laws:

Current Law (KCL): Total current entering a junction equals total current leaving.

Voltage Law (KVL): Sum of voltage drops in a loop is zero.

Practice Questions

1. (Multiple Choice) In a parallel circuit, adding more resistors:

a) Increases total resistance

b) Decreases total resistance

c) Has no effect

d) Increases total voltage

Answer: b) Decreases total resistance

2. (Short Answer) How does current split in a parallel circuit?

3. (Numerical) Find the total resistance of two resistors, 6Ω and 3Ω, in parallel.

Answer:

4. (Research-Based) How are Kirchhoff’s laws applied in real-life electrical networks?

5. (Critical Thinking) Why does a short circuit cause excessive current flow?

6. (Scenario-Based) A circuit with a 9V battery has three 3Ω resistors in series. Find the current.

7. (Essay Question) Explain the differences between series and parallel circuits in electrical systems.

8. (Data Analysis) Given voltage and current readings, analyze and find missing resistor values.

9. (Short Answer) What happens to total resistance if more resistors are added in series?

10. (Numerical) A 12V battery powers a circuit with a 4Ω resistor in series with a parallel combination of two 6Ω resistors. Find the total current.

6. Magnetic Fields and Sources of Magnetic Fields

Summary

Magnetic Field (B): A region where a force acts on moving charges. Measured in Tesla (T).

Right-Hand Rule: Determines force direction on a moving charge.

Magnetic Force on a Moving Charge:

Biot-Savart Law: Determines the magnetic field due to a current element.

Ampere’s Law:

Solenoids and Toroids: Generate uniform magnetic fields inside their coils.

Practice Questions

1. (Multiple Choice) The SI unit of the magnetic field is:

a) Newton

b) Tesla

c) Weber

d) Ampere

Answer: b) Tesla

2. (Short Answer) Why does a moving charge experience a force in a magnetic field but a stationary charge does not?

3. (Numerical) A charge of 2C moves at 4m/s perpendicular to a 3T magnetic field. Find the force.

Answer:

4. (Research-Based) How do MRI machines use magnetic fields?

5. (Critical Thinking) If a proton and an electron enter a uniform magnetic field with the same velocity, how will their paths differ?

6. (Scenario-Based) A current-carrying wire in a magnetic field experiences a force. What happens if the current direction is reversed?

7. (Essay Question) Explain the relationship between electricity and magnetism using Maxwell’s equations.

8. (Data Analysis) Given a table of current values and their resulting magnetic fields, determine the proportionality constant.

9. (Short Answer) What is the shape of the magnetic field around a long straight current-carrying wire?

10. (Numerical) A solenoid with 500 turns per meter carries a 3A current. Find the magnetic field inside it ().

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