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There are 27 drops of a conducting fluid. Each drop has radius r, and each of them is charged to the same potential V₁.They are then combined to form a bigger drop.The potential of the bigger drop is V₂ .Find the ratio V₂/V₁. [Ignore the change in density of the fluid on combining the drops].

Answer: Let Charge on each drop = q Charge on big drop = Q = 27q Radius of bigger drop = R . ∴ R = 3r . . . . V2 =... View Article

A thin rectangular magnet suspended freely has a period of oscillation equal to T. Now it is broken into two equal halves (each having half of the original length) and one piece is made to oscillate freely in the same field. if its period of oscillation is T’, the ratio T’/T is_______

Answer: A thin rectangular magnet suspended freely has a period of oscillation equal to T. Now it is broken into two equal halves (each having... View Article

A series LCR circuit is connected to an ac voltage source. When L is removed from the circuit, the phase difference between current and voltage is 3π. If instead C is removed from the circuit, the phase difference is again 3π between current and voltage. The power factor of the circuit is (1) 0.5 (2) 1.0 (3) -1.0 (4) zero

Answer:(2) 1.0 An LCR circuit is also known as a resonant circuit or tuned circuit. It consists of an inductor-L, capacitor-C, and resistor-R... View Article

A positively charged particle is released from rest in an unform electric field. The electric potential energy of the charge (1) remains a constant because the electric field is uniform. (2) increases because the charge moves along the electric field. (3) decreasases because the charge moves along the electric field (4) decreases because the charge moves opposite to the electric field.

Answer: (3) decreasases because the charge moves along the electric field When a positively charged particle in a uniform field is released from... View Article

An open pipe is in resonance in 2nd harmonic with frequency f₁. Now one end of the tube is closed and frequency is increased to f₂ such that the resonance again occurs in nth harmonic. Choose the correct option. (A) n = 5, f₂ = (5/4)f₁ (B) n = 3, f₂ = (3/4)f₁ (C) n =5, f₂ = (3/4)f₁ (D) n =3, f₂ = (5/4)f₁

An open pipe is in resonance in 2nd harmonic with frequency f<sub>1</sub>. Now one end of the tube is closed and frequency is... View Article

A resistance R is to be measured using a meter bridge. Student chooses the standard resistance S to be 100Ω. He finds the null point at l₁ = 2.9cm. He is told to attempt to improve the accuracy. Which of the following is a useful way? (1) He should measure l1 more accurately (2) He should change S to 1000Ω and repeat the experiment (3) He should change S to 3Ω and repeat the experiment (4) He should give up hope of a more accurate measurement with a meter bridge

Answer: (3) He should change S to 3Ω and repeat the experiment The balance of a metre bridge is always maintained. The long wire in a... View Article

Two uniform strings A and B made of steel are made to vibrate under the same tension. If the first overtone of A is equal to the second overtone of B and if the radius of A is twice that of B, the ratio of the length of the strings is (1) 1:2 (2) 1:3 (3) 1:4 (4) 1:5

Answer: (2) 1:3 Frequency of A = n1 Frequency of B = n2 ∴ 2n1 = 3n2 or . Where m = mass/length m = (cross sectional area × l × ρ)/l m... View Article

When a particle moves in a circle with a uniform speed (1) Its velocity and acceleration are both constant (2) Its velocity is constant but the acceleration changes (3) Its acceleration is constant but the velocity changes (4) Its velocity and acceleration both change.

Answer: (4) Its velocity and acceleration both change. In uniform circular motion speed is constant, but the direction is changing at each point... View Article

When a charged particle moves perpendicular to a magnetic field, then (1) Speed of the particle is changed. (2) Speed of the particle remains unchanged. (3) Direction of the particle remains unchanged. (4) Acceleration of the particle remains unchanged.

Answer:(2) Speed of the particle remains unchanged. A force acting on a particle is said to perform work when there is a component of the force... View Article

The conversion of a moving coil galvanometer into a voltmeter is done by (1) introducing a resistance of large value in series (2) introducing a resistance of small value in parallel (3) introducing a resistance of large value in parallel (4) introducing a resistance of small value in series

The conversion of a moving coil galvanometer into a voltmeter is done by (1) introducing a resistance of large value in series (2) introducing a... View Article

A long straight wire carrying a current of 30A is placed in an external uniform magnetic field of induction 4×10^-4T. The magnetic field is acting parallel to the direction of the current. The magnitude of the resultant magnetic induction in tesla at a point 2.0cm away from the wire is : [μ0 = 4π×10^-7Hm^-1] (1) 10^-4 (2) 3×10^-4 (3) 5×10^-4 (4) 6×10^-4

A long straight wire carrying a current of 30A is placed in an external uniform magnetic field of induction 4×10<sup>-4</sup>T.... View Article

A refrigerator works between 4⁰C and 30⁰C. It is required to remove 600 calories of heat every second in order to keep the temperature of the refrigerated space constant. The power required is:(Take 1cal = 4.2Joules) (1) 2.365W (2) 23.65W (3) 236.5W (4) 2365W

Answer: (3) 236.5W Given T2 = 40C = 4 + 273 = 277 K T1 = 300C = 30 + 273 = 303 K Q2 = 600 cal/sec Q2 = 600 × 4.2 Q2 = 2520 J/sec The... View Article

A lift is coming from 8th floor and is just about to reach 4th floor. Taking ground floor as origin and positive direction upwards for all quantities, which one of the following is correct? (1) x < 0, v < 0, a > 0 (2) x > 0, v < 0, a < 0 (3) x > 0, v < 0, a > 0 (4) x > 0, v > 0, a < 0

Answer: (1) x < 0, v < 0, a > 0 Displacement = Downward (x<0) Velocity = Downward (v<0) Acceleration = In direction of... View Article

A long solenoid has 500 turns. When a current of 2 amperes is passed through it, the resulting magnetic flux linked with each turn of the solenoid is 4×10^-3 Web. The self-inductance of the solenoid is (1) 1.0 henry (2) 4.0 henry (3) 2.5 henry (4) 2.0 henry

A long solenoid has 500 turns. When a current of 2 amperes is passed through it, the resulting magnetic flux linked with each turn of the... View Article

A spherical conductor of radius 10 cm has a charge of 3.2×10^-7C distributed uniformly. What is the magnitude of electric field at a point 15cm from the centre of the sphere? (1/4π∈⁰= 9 × 10⁹Nm/C²) (1) 1.28 × 10⁵N/C (2) 1.28 × 10⁶N/C (3) 1.28 × 10⁷N/C (4) 1.28 × 10⁴N/C

Answer: (1) 1.28 × 105 N/C Given: The charge present inside the sphere (q) = 3.2×10-7C The electric field is to be determined at a point at... View Article

Positive deviation from ideal behaviour takes place because of (1) molecular interaction between atoms and PV/nRT>1 (2) molecular interaction between atoms and PV/nRT<1 (2) finite size of atoms and PV/nRT>1 (4) finite size of atoms and PV/nRT<1

Answer: (1) molecular interaction between atoms and PV/nRT>1 Gases have a tendency to deviate from their ideal behaviour, and there are two... View Article

A charged particle moves through a magnetic field perpendicular to its direction. Then (1) kinetic energy changes but the momentum is constant (2) The linear momentum changes but the kinetic energy is constant (3) Both linear momentum and kinetic energy of the particle are not constant (4) Both linear momentum and kinetic energy of the particle are constant

Answer: (2) The linear momentum changes but the kinetic energy is constant The path of motion of a charge particle approaching a magnetic field... View Article

An insect trapped in a circular groove of radius 12 cm moves along the groove steadily and completes 7 revolutions in 100 sec. What is the angular speed and linear speed of motion? (1) 0.11 rad/s, 3.28 cm/s (2) 0.40 rad/s, 5 cm/s (3) 0.44 rad/s, 5.28 cm/s (4) None of these

Answer: (3) 0.44 rad/s, 5.28 cm/s Circular groove of radius = 12 cm Insects completes 7 revolutions in 100 sec The time period of... View Article

When no current is passed through a conductor (1) the free electrons do not move (2) the average speed of a free electron over a large period of time is zero (3) the average velocity of a free electron over a large period of time is zero (4) the average of the velocities of all the free electrons at an instant is zero

Answer: (3) the average velocity of a free electron over a large period of time is zero (4) the average of the velocities of all the free... View Article

The deflection in a moving coil galvanometer is (1) Directly proportional to the torsional constant (2) Directly proportional to the number of turns in the coil (3) Inversely proportional to the area of the coil (4) Inversely proportional to the current flowing

Answer: (2) Directly proportional to the number of turns in the coil A moving coil galvanometer is an instrument which is used to measure... View Article

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