# Variation of Intensity in Space

## Trending Questions

**Q.**

Two coherent narrow slits emitting sound of wavelength λ in the same phase are placed parallel to each other at a small separation of 2λ. The sound is detected by moving a detector on the screen E at a distance D(>>λ) from the slit S, as shown in figure (16-E6). Find the distance x such that the intensity at P is equal to the intensity at O.

**Q.**Two coherent sources of sound, S1 and S2, produce sound waves of the same wavelength λ=1 m, in phase. S1 and S2 are placed 1.5 m apart (see fig.). A listener, located at L, directly in front of S2 finds that the intensity is a minimum where he is 2 m away S2. The listener moves away from S1, keeping his distance from S2 fixed. The adjacent maximum of intensity is observed when the listener is at a distance d from S1. Then d is

- 12 m
- 5 m
- 2 m
- 3 m

**Q.**Two towers on top of two hills are 40 km apart. The line joining them passes 50 m above a hill halfway between the towers. What is the longest wavelength of radio waves, which can be sent between the towers without appreciable diffraction effects?

**Q.**The intensity of a sound wave gets reduced by 20% on passing through a slab. The reduction in intensity on passage through two such consecutive slabs is

- 50%
- 30%
- 40%
- 36%

**Q.**Sound waves of wavelength λ travelling in a medium with a speed of v m/s enter into another medium where its speed is 2v m/s. Wavelength of sound waves in the second medium is

- λ
- 2λ
- 4λ
- λ/2

**Q.**Figure shows two coherent sources S1 and S2 which emit sound of wavelength λ in phase. The separation between the source is 3λ. A circular wire of large radius is placed in such a way that S1S2 lies in its plane and the midpoint of S1S2 is at the centre of the wire. Find the number of angular positions θ(θ<90∘) on the wire for which constructive interference takes place.

**Q.**A small source of sound moves on a circle as shown in the figure and an observer is standing on O. Let n1, n2 and n3 be the frequencies heard when the source is at A, B and C respectively. Then

- n1>n2>n3
- n2>n1>n3
- n1=n2>n3
- n2>n3>n1

**Q.**An EM wave radiates outwards from a dipole antenna, with Eo as the amplitude of its electric field vector. The electric field Eo which transports significant energy from the source falls off as:

- Remains constant
- 1r3
- 1r
- 1r2

**Q.**Two interfering waves have intensities in the ratio 9 :1. Then the ratio of maximum to maximum intensity is:

- 16 :4
- 4 :2
- 100 :64
- 10 :8

**Q.**Two waves in the same medium are represented by y−t curves in the figure. Find the ratio of their average intensities.

- 45
- 54
- 2516
- 1625

**Q.**An observer approaches towards a stationary source of sound at constant velocity and recedes away at the same speed. The graph of wavelength observed with time is:

**Q.**Sound waves of frequency 320 Hz are sent into the top of a vertical tube containing water at a level that can be adjusted. Standing waves are produced at two successive water levels 44 cm and 74 cm from open end. The distance (in cm) of nearest displacement antinode from open end is

**Q.**

Two cars $\mathrm{A}$ and $\mathrm{B}$ are moving away from each other in opposite directions. Both the cars are moving at a speed of $20\mathrm{m}/\mathrm{s}$ with respect to the ground. If an observer in car $\mathrm{A}$ detects a frequency of $2000\mathrm{Hz}$ of the sound coming from car $\mathrm{B}$, what is the natural frequency of the sound source in car $\mathrm{B}$? (speed of sound in air $=340\mathrm{m}/\mathrm{s}$)

$2250\mathrm{Hz}$

$200\mathrm{Hz}$

$2300\mathrm{Hz}$

$2150\mathrm{Hz}$

**Q.**The faintest sound that can be heard has a pressure amplitude of about 4×10−5 N/m2 and the loudest that can be heard without pain has a pressure amplitude of about 2.8 N/m2. Determine the intensity of the faintest sound (both in W/m2 and in dB).

[Assume, air density is 1.3 kg/m3 and velocity of sound is 330 m/s and take log101.86=0.269]

- 2×10−12 W/m2, 1 dB
- 1.86×10−12 W/m2, 1.6 dB
- 1.86×10−12 W/m2, 2.7 dB
- 2×10−12 W/m2, 2.7 dB

**Q.**The velocity of electromagnetic waves in a dielectric medium (εr=4) is

- 7.5×107 meter /second
- 6×108 meter /second
- 1.5×108 meter /second
- 3×108 meter /second

**Q.**Sound waves are emitted uniformly in all directions from a point source. The dependence of sound level β in decibels on the distance r can be expressed as (a and b are positive constants)

- β=a−br2
- β=a−b (logr)2
- β=a−blogr
- β=−b logr2

**Q.**When a person wears a hearing aid, the sound intensity level increases by 30 dB. The sound intensity increases by

**Q.**A and B are two wave trains shown in the figure, the ratio of intensity of A to B is

- 1
- 2
- 4
- 8

**Q.**A long string of mass per unit length 0.2 Kg/m is stretched to a tension 500 N. A transverse wave of amplitude A = 10 mm and λ = 0.5 m is travelling on this string. This string is joined to another string of same cross section and mass per unit length 0.8 kg/m. The fraction of the average power carried by the wave in the first string that is transmitted to the second string is K/9. Find K.

**Q.**Two coherent point sources S1 and S2 vibrating in phase emit light of wavelength λ. The separation between the sources is 2λ. Consider a line passing through S2 and perpendicular to the line S1S2. Find the position of farthest minima.

- D=λ2

- D=15λ12

- D=15λ4

- D=λ3

**Q.**

A sound made on the surface of a lake takes $3s$ to reach a boatman. How much time will it take to reach a diver inside the water at the same depth?

Velocity of sound in air $=330m{s}^{-1}$

Velocity of sound in water $=1450$

**Q.**An electromagnetic wave of frequency 1×1014 Hertz is propagating along z-axis. The amplitude of electric field is 4 V/m. If ∈0=8.8×10−12 C2/N−m2, then average energy density of electric field will be:

- 35.2×10−12 J/m3
- 35.2×10−11 J/m3
- 35.2×10−10 J/m3
- 35.2×10−13 J/m3

**Q.**Light of intensity 10–5W/2 falls mon a sodium photocell of surface area 2 cm2 . Assuming that the top 5 layers of sodium absorb the incident energy, estimate time required for photoelectric emission in the wave-picture of radiation. The work function for the metal is given to be about 2 eV. What is the implication of your answer?

**Q.**

Number of waves of orange light emitted by krypton in 1 m is ____________.

**Q.**In the figure below, P and Q are two equally intense coherent sources emitting radiation of wavelength 20 m. The separation between P and Q is 5 m and the phase of P is ahead of that of Q by 90∘.A, B and C are three distinct points of observation, each equidistant from the midpoint of PQ. The intensities of radiation at A, B, C will be in the proportion,

- 0:1:4
- 2:1:0
- 0:1:2
- 4:1:0

**Q.**A person is standing at a distance D from an isotropic point source of sound. He walks 50.0 m towards the source and observes that the intensity of the sound has doubled. His initial distance D from the source is

- 50√2−1 m

- 50√2 m

- 100√2 m

- 50√2√2−1 m

**Q.**Sinusoidal waves 5.00 cm in amplitude are to be transmitted along a string having a linear mass density equal to 4.00×10−2kg/m. If the source can deliver a maximum power of 90 W and the string is under a tension of 100 N, then the highest frequency at which the source can operate it, is (take π2=10)

- 62.3 Hz
- 30 Hz
- 45.3 Hz
- 50 Hz

**Q.**The same progressive wave is represented by two graphs I and II. Graph l shows how the displacement y varies with the distance x along the wave at a given time. Graph II shows how y varies with time t at a given point on the wave. The ratio of measurements AB to CD, marked on the curves, represents

- wave number k
- frequency v
- wave speed V
- angular frequency ω

**Q.**A transverse wave is propagating along +x direction. At t=2s, the particle at x=4 m is at y=2 mm. With the passage of time, its y coordinate increases and reaches to a maximum of 4 mm. The wave equation is (Using ω and k with their usual meanings)

- y=4sin[ω(t−2)−k(x−4)+π6]
- y=4sin[ω(t+2)+k(x)+π6]
- y=4sin[ω(t−2)−k(x−4)+5π6]
- y=4sin[ω(t+2)+k(x−2)+π6]

**Q.**Change in temperature of the medium changes