Physics Chapter 4 Entry test MCQs
26. Which parameter get affected after superposition?
a. Frequency
b. Amplitude
c. Direction
d. Wavelength
27. The frequency of the first harmonic of a string stretched between two points is 100 Hz. The frequency of the third overtone is
a. 300 Hz
b. 200 Hz
c. 600 Hz
d. 400 Hz
28. “Stationary waves” are so called because in them
a. The particles of the medium do not execute SHM
b. The particles of the medium are not disturbed
c. The interference effect can’t be observed
d. There occurs no flow of energy along the wave
29. The frequency of the nth mode of vibration of a string stretched by a tension T and having mass m and length is given by
a. fn n/2 √lt/m
b. fn = n/2 √T/ml
c. fn= n/2 √T/m
d. fn = n/2l √T/m
30. If the string vibrates in ‘n’ loops, the wavelength is given by
a. λn = 2l/n
b. λn = 2/nl
c. λn = l/2n
d. None of these
31. If the successive overtones of a vibrating string clamped at its ends are 280 Hz and 350 Hz, the frequency of fundamental is:
a. 280 Hz
b. 350 Hz
c. 70 Hz
d. 140 Hz
32. If the number of loops of a stationary wave are increasing, then
a. λ decreases
b. λ increases
c. λ may increase or decrease
d. λ remains same
33. A string of length 2m fix between two supports vibrates in two loops. The distance between node and annode is:
a. 200 cm
b. 50 cm
c. 10 cm
d. 100 cm
34. The distance between two particles in a wave motion in the same phase is
a. 3λ/4
b. λ/4
c. λ
d. λ/2
35. The phase between two consecutive antinodes is:
a. π
b. π/4
c. 2π
d. π/2
36. When the string vibrates in three loops then the length ‘l’ of the string is expressed as
a. l = λ/2
b. l = 3λ/4
c. l = 2λ/3
d. l = 3λ/2
37. Consider a stretched string under tension and fixed at both ends. If the tension is doubled and the cross-sectional area halved, then the frequency becomes
a. Four times
b. Twice
c. Eight times
d. Half
38. When the antinodes are all at their extreme displacements, the energy stored is
a. Thermal energy
b. P.E
c. Κ.Ε
d. All of these
39. When an observer moves towards source with a velocity u0, then the modified frequency ‘fA’ becomes
a. fA = (v + uo)/2)f
b. fA = f(v – uo)
c. fA =(v-uo/v)f
d. fA =f(v+uo/v)
40. Doppler’s effect is not applicable for:
a. Electromagnetic waves
b. Microwaves
c. Standing waves
d. Ultrasonic
41. Doppler shift in frequency does not depend upon
a. The distance of the source from the listener
b. The actual frequency of the wave
c. The velocity of the observer
d. The velocity of the source
42. The source is moving towards a stationary observer then the pitch of the sound will
a. Remains constant
b. Sometimes increases and sometimes decreases
c. Increase
d. Decrease
43. The apparent frequency of the whistle of an engine changes in the ratio 6:5 as engine passes a stationary observer. If the speed of sound is 352 m/s. Then the speed of engine will be
a. 32 m/s
b. 22 m/s
c. 36 m/s
d. 27 m/s
44. A source of sound moves towards a stationary observer with a speed one third that of sound. If the frequency of the sound from the source is 100 Hz, the apparent frequency of the sound heard by the observer is
a. 150 Hz
b. 67 Hz
c. 75 Hz
d. 100 Hz
45. If a Radar system designed in accordance with the Doppler’s effect, if an airplane is moving away from a Radar, the wavelength of the reflected wave from the air plane would be:
a. Larger than the transmitting wave
b. Smaller than the transmitting wave
c. Either smaller or larger than the transmitting wave
d. Same as that of the transmitting wave
46. Stars moving towards earth shows
a. No shift
b. Blue shift
c. May be ‘A’ may be ‘B’ depending upon speed of stars
d. Red shift
47. Bats navigate and find food by
a. Amplitude
b. Ultrasonic
c. Refraction
d. Echo location
48. Which one of the following explains that all the galaxies are receding from us?
a. Neutrons stars
b. White shift
c. Red shift
d. Black holes
49. A whistle giving out 450Hz approaches a stationary observer at a speed of 33m/s. The frequency heard by the observer in Hz is (speed of sound = 330m/s).
a. 429
b. 409
c. 500
d. 517
50. The source of sound generating of a frequency of 3 kHz reaches an observer with a speed of 0.5 times the velocity of sound in air. The frequency heard by the observer is?
a. 3 kHz
b. 1 kHz
c. 6 kHz
d. 4 kHz