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UPSC Exam Instructions for Candidates

The Civil Services Examination is conducted in three stages - Prelims, Mains and Interview by UPSC. Before each stage, an application has to be... View Article

How to Apply for UPSC Online?

The Union Public Service Commission invites applications from the eligible candidates for Civil Services Examination once a year to recruit for... View Article

UPSC Application 2022 Window Open and Close Dates in Detail | UPSC Exam 2022

The Union Public Service Commission is the body responsible for conducting the IAS Exam. Candidates looking forward to appearing for the upcoming... View Article

01 Feb 2022: UPSC Exam Comprehensive News Analysis

CNA 01 Feb 2022:- Download PDF Here TABLE OF CONTENTS A. GS 1 Related B. GS 2 Related POLITY 1. The limits of the legislature’s power to suspend... View Article

International Relations This Week: Episode 59

International relations is a very important segment of the UPSC syllabus. In this series, we present an analysis of the most important... View Article

A stationary source is an emitting sound at a fixed frequency f₀, which is reflected by two cars approaching the source. The difference between the frequencies of sound reflected from the cars is 1.2% of f₀. What is the difference in the speeds of the cars (in km per hour) to the nearest integer? The cars are moving at constant speeds much smaller than the speed of sound which is 330 ms^-1.

1) 7.128 km/h 2) 7 km/h 3) 8.128 km/h 4) 9 km/h Answer: 2) 7 km/h Solution: f' = f0 (v + vc/v) f'' = f'(v/v - vc)... View Article

In an experiment with sonometer a tuning fork of frequency 256 Hz resonates with a length of 25 cm and another tuning fork resonates with a length of 16 cm. Tension of the string remaining constant. The frequency of the second tuning fork is

1) 163.84 Hz 2) 400 Hz 3) 320 Hz 4) 204.8 Hz Answer: 2) 400 Hz Solution: F = (1/2L)√(T/m) F ∝ 1/L F = k/L... View Article

A car moving with a velocity of 36 kmh ^-1 crosses a siren of frequency 500 Hz. The apparent frequency of siren after passing it will be

1) 520 Hz 2) 485 Hz 3) 540 Hz 4) 460 Hz Answer: 2) 485 Hz Solution: Given velocity of the car = 36 km/h = 36000/3600 = 10 m/s... View Article

A bus is moving with a velocity of 5 ms^-1 towards a huge wall. The driver sounds a horn of frequency 165 Hz. If the speed of sound in air is 335 ms^-1, the number of beats heard per second by a passenger inside the bus will be

1) 3 2) 4 3) 5 4) 6 5) 7 Answer: 3) 5 Solution: Apparent frequency, f'=f(v+vo)/(v−vs)... View Article

With what velocity should an observer approach stationary sound source, so that the apparent frequency of sound should appear double the actual frequency? (v is the velocity of sound)

1) v/2 2) 3v 3) 2v 4) v Answer: 4) v Solution: Given, f' = 2f f' = f[(v + v0)/(v + vs)] 2f = f[(v + v0)/(v)] 2v =... View Article

The speed of sound in air is 340 m/s. The speed with which a source of sound should move towards a stationary observer so that the apparent frequency becomes twice the original is

1) 640 ms-1 2) 340 ms-1 3) 170 ms-1 4) 85 ms-1 Answer: 3) 170 ms-1 Solution: Original frequency = f0 2f0 = f0[(v ±... View Article

The fundamental frequency of a segment of wire vibrating is 450 Hz and it is under a tension of 9 kg–wt. Then, tension at which the fundamental frequency of the same wire becomes 900 Hz is

1) 36 kg–wt 2) 27 kg–wt 3) 18 kg–wt 4) 72 kg–wt Answer: 1) 36 kg–wt Solution: n1 = k√T1 n2... View Article

A string fixed at both ends oscillates in 5 segments, length 10 m and the velocity of the wave is 20 ms^-1. What is the frequency?

1) 5 Hz 2) 15 Hz 3) 10 Hz 4) 2 Hz Answer: 1) 5 Hz Solution: 5λ/2=L ⇒5λ/2=10 m Therefore,... View Article

When the length of the vibrating segment of a sonometer wire is increased by 1%, the percentage change in its frequency is

1) 100/101 2) 99/100 3) 1 4) 2 Answer: 3) 1 Solution: f = (1/2l)√(T/μ) Take log and differentiate, we get... View Article

An open organ pipe is closed suddenly with the result, that the second overtone of the closed pipe is found to be higher in frequency by 100 than the first overtone of the original pipe. Then, the fundamental frequency of the open pipe is

1) 200 s-1 2) 100 s-1 3) 300 s-1 4) 250 s-1 5) 150 s-1 Answer: 1) 200 s-1 Solution: Frequency of second overtone (fifth... View Article

A glass tube of length 1.0 m is completely filled with water. A vibrating tuning fork of frequency 500 Hz is kept over the mouth of the tube and the water is drained out slowly at the bottom of the tube. If the velocity of sound in air is 330 ms^-1, then the total number of resonances, that occur will be

1) 2 2) 3 3) 1 4) 5 5) 4 Answer: 2) 3 Solution: λ = v/f = 330/500 = 0.66 m The resonance lengths are l1... View Article

The distance between nodes on a string is 5 cm. The velocity of the transverse wave is 2 ms ^-1. Then the frequency is

1) 5 Hz 2) 10 Hz 3) 20 Hz 4) 15 Hz Answer: 3) 20 Hz Solution: Distance between two nodes is λ/2 Therefore,... View Article

A closed organ pipe and an open organ pipe are tuned to the same fundamental frequency. The ratio of their lengths is

1) 1 : 1 2) 2 : 1 3) 1 : 4 4) 1 : 2 Answer: 4) 1 : 2 Solution: Avoiding end correction, the length of closed organ pipe, is... View Article

The frequency of the fundamental note in a wire stretched under tension T is f. If the tension is increased to 25 T. then the frequency of the fundamental note will be

1) 25f 2) 5f 3) 10f 4) f Answer: 2) 5f Solution: The fundamental frequency f=(1/2L)√(T/m) Therefore,... View Article

Two stretched strings have lengths l and 2l while tensions are T and 4T respectively. If they are made of same material, the ratio of their frequencies is

1) 2 : 1 2) 1 : 2 3) 1 : 1 4) 1 : 4 Answer:3) 1 : 1 Solution: Frequency is given by f=(1/2l)√(T/μ) Therefore, First... View Article