A wave travelling along the x-axis is described by the equation y(x, t) = 0.005 cos (αx −βt). If the wavelength and the time period of the wave are 0.08 m and 2.0 s, respectively, then α and β in appropriate units are 

• α = 25.00 π, β = π

• α = 0.08/ π,  2.0/π

• α = 0.04 / π , β =1.0/π

• α = 12.50 , β =π/ 2.0

A whistle producing sound waves of frequencies 9500 Hz and above is approaching a stationary person with speed v ms⁻¹. The velocity of sound in air is 300 ms−1. If the person can hear frequencies upto a maximum of 10,000 Hz, the maximum value of v upto which he can hear the whistle is

• 
• 

• 15 ms^-1

• 30 ms^-1

C.

15 ms^-1

An observer is moving with half the speed of light towards a stationary microwave source emitting waves at frequency 10 GHz. What is the frequency of the microwave measured by the observer?
(speed of light = 3 × 10⁸ ms^–1)

• 17.3 GHz

• 15.3 GHz

• 10.1 GHz

• 12.1 GHz

An observer moves towards a stationary source of the sound, with a velocity one-fifth of the velocity of sound. What is the percentage increase in the apparent frequency?

• 0

• 0.5%

• 5%

• 20%

D.

20%

In amplitude modulation, sinusoidal carrier frequency used is denoted by ω_c and the signal frequency is denoted by ωm. The bandwidth (Δω_m) of the signal is such that Δω_m << ω_c. Which of the following frequencies is not contained in the modulated wave?

• ωm + ωc

• ωc - ωm

• ωm

• ωc