A soap bubble of radius \(r\) is blown up to form a bubble of radius \(2r\) under isothermal conditions. If \(T\) is the surface tension of the soap solution, the energy spent in the blowing is:
1. \(3\pi Tr^2\)
2. \(6\pi Tr^2\)
3. \(12\pi Tr^2\)
4. \(24\pi Tr^2\)
1. \(3\pi Tr^2\)
2. \(6\pi Tr^2\)
3. \(12\pi Tr^2\)
4. \(24\pi Tr^2\)
Subtopic: Surface Tension |
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A current of \(1.6\) A is passed through a solution of CuSO4. How many Cu++ ions are liberated in one minute? (Electronic charge= \(1.6\times10^{-19}\) C)
1. 3 × 1020
2. 3 × 1010
3. 6 × 1020
4. 6 × 1010
Subtopic: Current & Current Density |
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A magnetic field exerts no force on:
| 1. | a magnet |
| 2. | an unmagnetised iron bar |
| 3. | a moving charge |
| 4. | stationary charge |
Subtopic: Lorentz Force |
86%
From NCERT
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In an \(LCR\) circuit inductance is changed from \(L\) to \(L/2.\) To keep the same resonance frequency, \(C\) should be changed to:
1. \(2C\)
2. \(\frac C2\)
3. \(4C\)
4. \(\frac C4\)
Subtopic: LC Oscillations (OLD NCERT) |
69%
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The sound waves after being converted into electrical waves are not transmitted as such because:
| 1. | they travel with the speed of sound. |
| 2. | the frequency is not constant. |
| 3. | they can, heavily absorbed by the atmosphere. |
| 4. | the height of antenna has to be increased several times. |
Subtopic: Types of Waves |
51%
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The tip of a needle does not give a sharp image on a screen. This is due to:
1. polarization
2. interference
3. diffraction
4. none of these
2. interference
3. diffraction
4. none of these
Subtopic: Diffraction |
58%
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An engine moving towards a wall with a velocity \(50\) m/s emits a note of \(1.2\) kHz. The speed of sound in air is \(350\) m/s. The frequency of the note after reflection from the wall as heard by the driver of the engine is:
1. \(2.4\) kHz
2. \(0.24\) kHz
3. \(1.6\) kHz
4. \(1.2\) kHz
Subtopic: Doppler's Effect (OLD NCERT) |
82%
From NCERT
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The surface temperature of the sun which has maximum energy emission at \(500\) nm is \(6000\) K. The temperature of a star which has maximum energy emission at \(400\) nm will be:
1. \(8500\) K
2. \(4500\) K
3. \(7500\) K
4. \(6500\) K
1. \(8500\) K
2. \(4500\) K
3. \(7500\) K
4. \(6500\) K
Subtopic: Wien's Displacement Law |
63%
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The truth table given below is for: (A and B are the inputs, Y is the output)
| A | B | Y |
| 0 | 0 | 1 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
1. NOR
2. AND
3. XOR
4. NAND
2. AND
3. XOR
4. NAND
Subtopic: Logic gates |
69%
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Two rectangular blocks A and B of masses \(2\) kg and \(3\) kg respectively are connected by a spring of spring constant \(10.8\) Nm-1 and are placed on a frictionless horizontal surface. Block A was given an initial velocity of \(0.15\) ms-1 in the direction shown in the figure. The maximum compression of the spring during the motion is:
1. \(0.01\) m
2. \(0.02\) m
3. \(0.05\) m
4. \(0.03\) m
Subtopic: Elastic Potential Energy |
55%
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