CBSE physics
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Two charges of magnitudes – 2Q and + Q are located at points (a, 0) and (4a, 0) respectively. What is the electric flux due to these charges through a sphere of radius ‘3a’ with its centre at the origin?
Using gauss law, we have
Electric flux is given by, 
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How does the mutual inductance of a pair of coils change when,
(i) distance between the coils is increased and
(ii) number of turns in the coils is increased?
Using the formula, 
i) Mutual inductance decreases when the distance between the coils is increased.
ii) Now using the formula,
On increasing the number of turns in the coil, mutual inductance also increases.
Two identical cells, each of emf E, having negligible internal resistance, are connected in parallel with each other across an external resistance R. What is the current through this resistance?
Internal resistance of the circuit is negligible.
So, total resistance is R.
Therefore, current across the circuit is given by, 
The motion of copper plate is damped when it is allowed to oscillate between the two poles of a magnet. What is the cause of this damping?
The changing magnetic flux through the plate produces a strong eddy current in the direction, which opposes the cause as the plate oscillates.
Welders wear special goggles or face masks with glass windows to protect their eyes from electromagnetic radiations. Name the radiations and write the range of their frequency.
The radiations are ultraviolet radiations.
The frequency range of UV rays is 1015 –1017Hz.
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Mock Test Series
Mock Test Series