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Directions: From the statements of Assertion and Reason mark the correct answer from the options.
(a) If both assertion and reason are true, and reason is the correct explanation of assertion.
(b) If both assertion and reason are true, but reason is not the correct explanation of assertion.
(c) If assertion is true, but reason is false.
(d) If both assertion and reason are false.
Assertion: Diamagnetic materials can exhibit magnetism.
Reason: Diamagnetic materials have permanent magnetic dipole moment.
Some materials when placed in an external magnetic field, acquire a very low magnetism in a direction opposite to the field. These materials when brought near the end of a strong magnet, they get repelled. These materials are diamagnetic and this property of materials is called the diamagnetism. This property is generally found in materials in which there are even number of electrons in their atoms (or molecules) and pairs are formed with two electrons. In each pair, the spin of one electron is in direction opposite to the spin of other electron. Hence, the electrons of each pair completely cancel the magnetic moment of each other. Thus, the net magnetic moment of each atom of such material is zero. Hence, option (c) is true.
For a certain radioactive substance, it is observed that after 4 hours, only 6.25% of the original sample is left undecayed. Which of the following statements is incorrect?
A police car horn emits sound at a frequency of 240 Hz when the car is at rest. If the speed of sound is 330 m/s, the frequency heard by an observer who is approaching the car at a speed of 11 m/s, is
The magnetic susceptibility of a material of a rod is 449. Permeability of vacuum is 4π x 10-7 henry/metre. The absolute permeability of the material of the rod (in henry/metre) is
A Carnot engine works as a refrigerator between 250 K and 300 K. If it receives 750 calories of heat from the reservoir at the lower temperature, then the amount of heat rejected at the higher temperature is
The threshold frequency for a metallic surface corresponds to an energy of 6.2 eV and the stopping potential for a radiation incident on this surface is 5 V. The incident radiation lies in
A long horizontal rod has a bead, which can slide along its length and is initially placed at a distance L from one end A of the rod. The rod is set in angular motion about A with constant angular acceleration α . If the coefficient of friction between the rod and the bead is and gravity is neglected, then the time after which the bead starts slipping is
Directions: The following question contains 4 choices (A), (B), (C) and (D), out of which ONLY ONE is correct
In the experiment to determine the speed of sound using a resonance column,
Correct Answer : prongs of the tuning fork are kept in a vertical plane
The figure shows variation of photocurrent with anode potential for a photosensitive surface for three different radiations. Let Ia, Iband Icbe the intensities and va, vband vcbe the frequencies for the curves a, b and c, respectively. Then,
The bob of a simple pendulum is a spherical hollow ball filled with water. A plugged hole near the bottom of the oscillating bob gets suddenly unplugged. During observation, till water is coming out, the time period of oscillation would
When water begins to come out, the centre of mass begins to lower. There is an increase in the effective length and hence an increase in the time period : When water flows out completely, the centre of mass begins to shift back to the geometrical centre of the follow bob. So, there is a decrease in the effective length and hence a decrease in time period. When water flows out completely, the centre of mass is again at the geometrical centre. Now, the time period is the same as in the beginning.
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