Latest Physical Science Reviewer 5

1. According to the effects of length contraction, from the viewpoint of an observer stationary with respect to a body moving at a uniform speed relative to the observer, which one is CORRECT?

A. The body contracts along the direction of the motion.

B. The time it takes for a clock incorporated in the body to tick contracts.

C. The body is not now contracted but would contract if it were accelerate.

D. The body contracts in some direction traverse to the direction of motion.

Ans: A. The body contracts along the direction of the motion.

-The Law of Contraction states that the length of any object an a moving frame will appear foreshortened in the direction of motion, or contracted. The amount of contraction can be calculated from the Lorentz transformation. The length is maximum in the frame in which object is at rest.

2. April and May are identical twins. One day, April embarked on a high-speed space travel into a distance star. When he gets back home, who is older between the two?

A. April

B. May

C. None of them because they are still of the same age

D. Cannot be determined

Ans: B. May

-In physics, the twin paradox is a thought experiment in special relativity involving identical twins, one of whom makes a journey into space in a high-speed rocket and returns home to find that the twin who remained on Earth has aged more.

3. An accelerated frame is a non-inertial frame. Is this TRUE?

A. True

B. False

C. Sometimes true, sometimes false

D. Not enough information given

Ans: A. True

-A non-inertial reference frame is undergoing acceleration with respect to an inertial frame. That is, an object whose position is judge from this frame will seem to spontaneously change its velocity with no apparent non-zero net force acting upon it. This completely violates  the law of inertia and Newton’s laws of motion, since these laws claim that the only way an object can change its velocity is if an actual non-zero net force is applied to the object.

4. What is the rest energy of a single proton which has a rest mass of 1.67 x 10 ^-27kg?

A. 1.50 x 10 J

B. 1.50 x 10¹ J

C. 1.50 x 10^-10J

D. 1.50 x 10^-10J

Ans: D. 1.50 x 10^-10J

-E = mc+²

 E = (1.67 x 10^-27 kg) (3.00 x 10⁸ m/s)²

    = 1.50 x 10^-10 J

5. Which of the following statements is TRUE about the speed of light?

A. The speed of light has a value that depends on the observer’s frame of reference.

B. The speed of light has the same value for observers in all reference frames.

C. The speed of light is constant in an inertial frame of reference.

D. The speed of light is slower in a moving frame of reference.

Ans: C. The speed of light is constant in an inertial frame of reference.

-See number 196 for the explanation

6. A person is riding a moped that is travelling at 20 m/s. What is the speed of the ball if the moped rider throws a ball forward at 4 m/s while riding the moped?

A. 16 m/s

B. 20 m/s

C. 24 m/s

D. 80 m/s

Ans: C. 24 m/s

-20m/s + 4m/s = 24m/s forward

7. According to Einstein, what is considered the fourth dimension?

A. Curled dimension

B. Horizontal dimension

C. Space dimension

D. Time dimension

Ans:  D. Time dimension

-Space consists of 3 dimensions, and time is 1-dimentional, space-time must, therefore be a 4-dimentional object.

8. As you observe a fish inside an aquarium, the fish appears to be bigger when underwater. When observed through the side, the fish seems closer than if you observe over the top. When you look through the corner, it appears to be that there are two fishes. What explains this observation?

A. Diffraction

B. Interference

C. Reflection  

D. Refraction

Ans: D. Refraction

-Refraction is the bending of a wave when it enters a medium where its speed is different. Since refraction of light occurs when it crosses the boundary, visual distortions often occur. These distortions occur when light changes medium as it travels from the object to our eyes.

9. What is the phenomenon by which the accident light falling on a surface is back into the same medium?

A. Absorption

B. Polarization

C. Reflection

D. Refraction

Ans: C. Reflection

-Reflection of light (and other form of electromagnetic radiation) occurs when the waves encounter a surface or other boundary that does not absorb the energy of the radiation and bounces the waves away from the surface.

10. Which property is responsible for alternating light and dark bonds when light passes through two or more narrow slits?

A. Diffraction

B. Interference

C. Polarization

D. Refraction

Ans: B. Interference

-Interference usually refers to the interaction of waves that are correlated or coherent with each other, either because they come from the same source or because they have the same or nearly the same frequency. Light, because of its wave properties, will show constructive and destructive interface. This was first shown in 1801 by Thomas Young, who sent sunlight through two narrow slits and showed that an interface pattern could be seen on a screen placed behind the two slits. The interference pattern was a set of alternating bright and dark lines, corresponding to where the light from one slit was alternately constructively and destructively interfering with the light from the second slit.

11. What happens when a light wave enters into a medium of different optical density?

A. Its speed and frequency change.

B. Its speed and wavelength change.

C. Its frequency and wavelength change.

D. Its speed, frequency and wavelength change.

Ans: B. Its speed and wavelength change.

-Like any wave, the speed of a light wave is dependent upon the properties of the medium. In the case of an electromagnetic wave, the speed of the wave depends upon the optical density of that material. The optical density of a material relates to the sluggish tendency of the atoms of a material to maintain the absorbed energy of an electromagnetic wave in the form of vibrating electrons before remitting it as a new electromagnetic disturbance. The more optically dense a material is, the slower that a wave will move through the material.

12. If carbon tetrachloride has an index of refraction of 1.461, what is the speed of light through this liquid? (c= 3.00 x 10⁸ m/s)

A. 1.46 x 10⁸ m/s

B. 2.05 x 10⁸ m/s

C. 4.38 x 10⁸ m/s

D. 4.46 x 10⁸ m/s

Ans: B. 2.05 x 10⁸ m/s

-n= c/v, therefore v=c/n    v=3.00 x 10⁸ m/s / 1.461 = 2.05 x 10⁸ m/s

13. A ray of light in air is incident of an air-to-glass boundary at an angle of 36 degrees with the normal. If the index of refraction of the glass is 1.65, what is the angle of the refracted ray within the glass with respect to the normal?

A. 18 degrees

B. 30 degrees

C. 46 degree

D. 56 degrees

Ans: A. 18 degrees

-Use Snell’s law:

                                      n_i * sine(Theta i) =   n_r * sine(Theta r)

where

                          n­_i=1.00 (in air), Theta i=30. Degrees, n_r = 1.65

Substitute and solve for Theta r.

                       Sine(Theta  r) = 1.00 * sine(30. Degrees) / 1.65 = 0.3030

                                Theta r = invsin(0.3030) = 17.6 degrees

14. If the critical angle for internal reflection inside a certain transparent material is found 48 degrees, what is the index of refraction of the material? ( air is outside the material )

A. 0.74

B. 1.35

C. 1. 48

D. 1.53

Ans: B. 1.35

- The critical angle is the angle of incidence (which is always in the more dense material) for which the angle of refraction is 90 degrees.

Apply this to Snell’s law equation:

                                        n_r = sine(48.0 deg) = 1.00 * sine (90 deg)

Solve for n_r.

                                                  n_r = 1.00 / sin(48.0 deg) = 1.35

15. According to the law of reflection, from what angle is light coming after it is reflected from a mirror?

A. The same angle as the incident ray as measured from the surface of the mirror

B.  The same angle as the incident ray as measured from the normal to the mirror

C.  Some light comes directly from the object and some passes through the mirror

D. Cannot be determined

Ans: B.  The same angle as the incident ray as measured from the normal to the mirror

-When a ray of light strikes a plane mirror, the light ray reflects off the mirror. Reflection involves a change in change of the light ray. The convention used to expressed the direction of a light ray  is to indicate the angle which the light ray makes with a normal line drawn to the surface of the mirror. The angle of incidence is the angle between this normal line and the reflected ray.

16. Two planed mirror are positioned perpendicular to each other. A ray of rad light incident on mirror at an angle of 55ᵒ . This ray is reflected from mirror 1 and then strikes 2 and is reflected again. The angle of reflection will be ___________.

A. 35ᵒ

B. 45ᵒ

C. 55ᵒ

D. 70ᵒ

Ans: A. 35ᵒ

-The angle of reflection is equal to the angle of incidence. The angle of incidence of mirror 2 is 90-55ᵒ = 35 ᵒ, so this is the angle of reflection.

17. A point object is placed in front of a plane mirror. Which is the correct location of the image by the mirror?

A. A

B. B

C. C

D. D

Ans: D.

-The plane mirror will produce an image of the object on the opposite side of the mirror. The distance from the object to the mirror equals the distance from the image to the mirror.

18. Which of the following is the BEST description of a white light?

A. It is a mixture of every color.

B. It is a mixture of seven color.

C. It is a mixture of red, blue and yellow.

D. It is a pure color that cannot be broken up.

Ans: A. It is a mixture of every color.

-White light is a light that contains all the wavelengths of visible light at approximately equal intensities as in sunlight or the light from white hot solids.

19. Which of the following observation is NOT true whenever a system is in chemical equilibrium?

A. Attainment of equilibrium requires time.

B. The rates of opposing reactions are equal.

C. The products do not change back to reactants.

D. Concentration remain constant at equilibrium even though the opposing reactions are continuing.

Ans: C. The products do not change back to reactants.

-The chemical equilibrium state describes concentrations of reactants and products in a reaction taking place in a closed system, which no longer change with time. It means that the rate of the forward reaction equals the rate of the reverse reaction, such that the concentration of reactants and products remain fairly stable in a chemical reaction. In theory, every forward reaction, there is subsequent reverse reaction.

20. Sunsets often appears to have a more reddish-orange color than noon. Which of the following phenomenon is responsible for this effect?

A. Rayleigh Scattering

B. Dispersion

C. Polarization

D. Refraction

Ans: A. Rayleigh Scattering

-Rayleigh Scattering is the elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the light. At sunrise and sunset the rays from the sun have to travel a larger part of the atmosphere than at noon. Therefore most of the blue light is scattered away and only the red light which is least scattered reaches the observer. Hence, sun appears reddish at sunrise and sunset.

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