Regents Physics 4 — Questions and Answers
Question 1: An electron moves perpendicular to a magnetic field. The magnetic force on the electron acts:
- In the same direction as its velocity
- Opposite to its velocity
- Perpendicular to both its velocity and the field (Correct answer)
- Parallel to the magnetic field
Correct answer: Perpendicular to both its velocity and the field
The magnetic force on a charged particle is F = qv × B, which is always perpendicular to both the velocity and the magnetic field.
Question 2: Which phenomenon provides evidence that light behaves as a wave?
- Photoelectric effect
- Diffraction (Correct answer)
- Nuclear fission
- Thermionic emission
Correct answer: Diffraction
Diffraction—the bending of light around obstacles—is a wave behavior that demonstrates the wave nature of light.
Question 3: A 60 W light bulb operates on a 120 V circuit. What is the current through the bulb?
- 0.5 A (Correct answer)
- 2 A
- 7,200 A
- 180 A
Correct answer: 0.5 A
P = IV, so I = P/V = 60/120 = 0.5 A.
Question 4: Which of the following best explains why a compass needle points north?
- The Earth has a gravitational pull toward the north pole
- The Earth acts as a giant magnet with a magnetic south pole near geographic north (Correct answer)
- The compass needle is attracted to oxygen in the atmosphere
- Magnetic field lines originate from the geographic north pole
Correct answer: The Earth acts as a giant magnet with a magnetic south pole near geographic north
Earth's geographic north pole is near its magnetic south pole; since opposite poles attract, the compass needle's north pole points toward it.
Question 5: An object in uniform circular motion experiences a centripetal acceleration directed:
- Tangent to the circle in the direction of motion
- Away from the center of the circle
- Toward the center of the circle (Correct answer)
- Perpendicular to the plane of the circle
Correct answer: Toward the center of the circle
Centripetal acceleration always points toward the center of the circular path.
Question 6: What is the index of refraction of a material in which light travels at 2.0 × 10⁸ m/s? (c = 3.0 × 10⁸ m/s)
- 0.67
- 1.5 (Correct answer)
- 2.0
- 6.0 × 10¹⁶
Correct answer: 1.5
n = c/v = (3.0 × 10⁸)/(2.0 × 10⁸) = 1.5.
Question 7: Which statement about momentum is correct for an isolated system?
- Momentum is always zero
- Momentum increases as kinetic energy increases
- Total momentum is conserved (Correct answer)
- Momentum equals mass times acceleration
Correct answer: Total momentum is conserved
The law of conservation of momentum states that in an isolated system, total momentum remains constant.
Regents Physics 4
An electron moves perpendicular to a magnetic field.
The magnetic force on the electron acts: