## Saturday, March 1, 2014

### GRE Sample Physics Problems (Conclusion):

If two colors of light (not pigments) are combined, one or other of two effects is noticed. If certain colors are mixed additively, such as red and yellow, the resulting hue is orange, which is the hue between them in the spectrum. If certain other colors such as red and blue-green are added, the result is white light.

Any two colors which, if added together, give white light are called complementary colors. Since all the colors added together give white light, they’re combination may be written symbolically as follows:

R + O + Y + G + B +  V   = W (white)

Also: R + BG = W  and B + V = W

91. From the preceding information it can be concluded that: O + Y + G + B + V gives:

A)    orange….B) red……C) white…….D) yellow…….E) blue-green

92.The combination of R + O + G + B + V gives:

A) blue……B) orange……C) red………D) white…….E) green

93. The shortest wavelength produced in an X-ray tube operated at 2 million volts would be: (1 Å  = 10 -10 m)

A) 1 Å  …..B) 0.15 Å…….C) 0.01 Å ……D) 10 -5  Å… E) 10 -4  Å

94. The de Broglie wavelength associated with neutrons in thermal equilibrium with matter at 300 K is approximately:

A)  179  Å…….B) 1790  Å…….. C) 17. 9  Å…..D) 0. 179  Å…..

E) 1. 79  Å

95.Two balls of equal mass are suspended as shown in the diagram below. The coefficient of restitution between the balls is equal to 0.5  Ball A after its release strikes ball B with a force just sufficient to send mass B to a position where the cord supporting it becomes horizontal. The angle q made by the cord supporting A in its initial position is given by:

A)    cos q = 0.5…..B) cos q = 0.25…..C) cos q = 1…..

D) sin q = 2/3….E) cos q = 1 - Ö3

96. At the instant of the collision of the two balls:

A)    the total kinetic energy is conserved

B)    The potential energy is decreased

C)    The Hamiltonian is conserved

D)   The kinetic energy is increased

E)    Part of the kinetic energy is changed to heat

97.If the coefficient of restitution was equal to 1, then we would have a completely elastic collision and assuming ball B is at rest when A collides with it:

A)    Ball A will be at rest after the collision

B)    Ball A will move with ball B in the same direction if sin q > 0.5

C)    Ball A will move in the opposite direction to ball B.

D)   Both balls will be at rest after the collision.

E)    Ball B will be in s standing position.

98. The electric (E-) field in an electromagnetic wave is described the relation:

E(r, t) = (e 1 E1 +  e 2 E2)  exp [ (ik r - iwt)

Where  e 1  and  e 2  are two  mutually orthogonal unit vectors, both of which are perpendicular to k, and  E1 and E2 are two real numbers. (For right circular polarization of an electric wave, the electric vector rotates in the clockwise direction when an observer faces into the oncoming wave).

This electromagnetic wave is:

A)    plane polarized……B) right circularly polarized

C) left circularly polarized……D) elliptically polarized    E) unpolarized

99. If:  E2  =  i E1  then the electromagnetic wave is:

B)    A) plane polarized…..B) right circularly polarized

C) left circularly polarized……D) elliptically polarized    E) unpolarized

100. A ray of light strikes at normal incidence a thin transparent film (index of refraction = n). Reinforcement of the reflected ray will occur when the film thickness, in terms of the wavelength of the incident light, equals:

A)    ¼  …..B) ¼  n ……C) ½   ….D) 1/ (2n)  ….E)  9/ (8n)