Test Prep Test Prep Certifications OAT Questions & Answers

• Question 221:

  Which of the following statements about refraction is true?

  A. Refraction means a change in direction of the wave.

  B. The angle of reflection equals the angle of refraction.

  C. The frequency in a refracted wave changes.

  D. The phase of a refracted wave changes.

  Correct Answer: A

  Refraction occurs when a wave enters a new medium. The boundary between the old medium and the new medium produces a reflected wave and a refracted wave. Since the medium is different, the speed and direction of the refracted wave changes. This changes the wavelength, but the frequency remains the same. The angle of reflection depends on the angle of incidence of the wave that strikes the boundary. The angle of refraction depends partly on this angle of incidence, but also on the indices of refraction of the two substances. Although refraction is defined as a wave changing direction when it enters a new substance, a wave will not change direction if it enters this new medium exactly perpendicular to the surface.

• Question 222:

  You blow up a rubber balloon and hold the opening tight with your fingers. You then release your fingers, causing air to blow out of the balloon. This pushes the balloon forward, causing the balloon shoots across the room. Which of Newton's laws best explains the cause of this motion?

  A. First law

  B. Second law

  C. Third law

  D. Law of gravity

  Correct Answer: C

  All three laws are operating, but the third law (forces come in equal and opposite pairs) best explains the motion. The first law (inertia) is shown from the fact that the balloon doesn't move until a force acts upon it. The second law (F = ma) is shown because you can see the force and the acceleration. The force comes from the contraction of the rubber balloon. The stretched rubber exerts a force on the air inside the balloon. This causes the air to accelerate in accordance with the second law. You can't see this acceleration because the air is invisible and because it is all the air in the room that the balloon is exerting a force on. However, the air in the room exerts and equal and opposite force on the balloon (this is Newton's third law), which causes the balloon to accelerate in the direction it did.

• Question 223:

  A lens forms an upright image 19 cm from a lens of an object 49 cm from the lens. The object and image are on the same side of the lens. What is the magnification of the image?

  A. 0.39

  B. 2.6

  C. 13.7

  D. 31.2

  Correct Answer: A

  The magnification of a lens can be calculated from its image distance, i, and its object distance, o. M = i /

  o. Here M = 19/49 = 0.39.

• Question 224:

  A solenoid is made of loops of wire, through which a current is run. What is the purpose of putting a lot if loops into a solenoid?

  A. To increase the magnetic field inside the solenoid.

  B. To increase the magnetic field outside the solenoid.

  C. To decrease the magnetic field inside the solenoid.

  D. To decrease the magnetic field inside the solenoid.

  Correct Answer: A

  Solenoids create a magnetic field inside the coils. Outside the solenoid, the magnetic field is practically zero, so increasing the number of coils won't have much effect on the exterior field strength. Inside the coils, increasing the number and density of coils increases the field strength.

• Question 225:

  Which of the following gives the correct order of electromagnetic radiation from the lowest frequency to the highest frequency?

  A. microwaves, UHF radio waves, x-rays, visible light

  B. UHF radio waves, microwaves, visible light, x-rays

  C. microwaves, visible light, x-rays, UHF radio waves

  D. microwaves, x-rays, visible light, UHF radio waves

  Correct Answer: B

  Radio waves have the lowest frequency and the longest wavelength. Microwaves also have low frequencies and long wavelengths compared to visible light. X-rays are highly energetic and have higher frequencies and smaller wavelengths than visible light.

• Question 226:

  An election moves in a uniform electric field in the same direction as the electric field from point A to point

  B. Which of the following statements is true?

  A. The potential energy of the electron decreased.

  B. The potential energy of the electron increased.

  C. The potential energy of the electron remained constant.

  D. The potential energy of the electron was converted into kinetic energy.

  Correct Answer: B

  The direction of the electric field is the same as the direction of the force on a positive test charge. Moving a negative charge in the direction of the electric field requires an external force to oppose the electric field. This would increase the electron's potential energy.

• Question 227:

  A manometer filled with mercury has a higher pressure on the open end, with a difference of 380 mm in the height of the fluid. What is the pressure of the gas in there?

  A. 100,000 Pa

  B. 75,000 Pa

  C. 50,000 Pa

  D. 25,000 Pa

  E. Cannot be determined.

  Correct Answer: C

  In manometers filled with mercury (Hg), the difference in height of the fluid is equivalent to the difference in pressure. There is a difference in 380 mmHg between the pressure inside and outside, which is half of the atmospheric pressure of 760 mmHg, or 1 atm. 1 atm is roughly 100,000 Pa, so the pressure inside is 50,000 Pa.

• Question 228:

  A helicopter shines its light into the ocean at an incidence angle of 30°. What is the angle of reflection?

  Assume index of refraction is n = 1.33 for water and n = 1 for air.

  A. 0°

  B. 15°

  C. 30°

  D. 60°

  E. Cannot be determined.

  Correct Answer: C

  This is a conceptual question that provides additional information to throw you off. Angle of incidence = Angle of reflection.

• Question 229:

  Rank the following in ascending order of wavelength magnitude:

  I. Gamma rays

  II. X-Rays

  III. Visible light

  IV.

  Radio waves

  A.

  III –andgt; I –andgt; II –andgt; IV

  B.

  I –andgt; II –andgt; III –andgt; IV

  C.

  II –andgt; I –andgt; IV –andgt; III

  D.

  IV –andgt; III –andgt; II –andgt; I

  E.

  II –andgt; I –andgt; III –andgt; IV

  Correct Answer: B

  The energy and frequency increases from Radio waves –andgt; Microwaves –andgt; IR –andgt; Visible light –andgt; UV –andgt; X-Rays –andgt; Gamma rays.

  But wavelength increases inversely, starting from Gamma rays (having the smallest wavelengths) to Radio waves (having the largest wavelengths)

• Question 230:

  A wire of resistance R is about to be replaced with a different wire that is three times as long and having a radius three times as much as the original wire. What is the resistance of this new wire?

  A. 1/2

  B. 1/4

  C. 1/3

  D. 1/5

  E. The resistance is the same in both wires.

  Correct Answer: C

  The resistance formula is R = p(L/A); where p = resistivity, L = length and r = radius.

  Tripling the length gives 3L, whereas tripling the radius would make the area 9x as big (A = 2pi × r2). Thus,

  you would end up with a ratio of 3/9, which is 1/3 the resistance of the new wire.