Two parallel plates have equal and opposite charge. When the space between them is evacuated, the electric field between the plates is 2 
. When the space is filled with dielectric, the electric field becomes 1 . The dielectric constant of the dielectric material
|
(a) 1/2 |
(b) 1 |
(c) 2 |
(d) 3 |
(c) 2
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In Bohr model of hydrogen atom, the ratio of periods of revolution of an electron in n = 2 and n = 1 orbits is
|
(a) 2 : 1 |
(b) 4 : 1 |
(c) 8 : 1 |
(d) 16 : 1 |
Why are red coloured lights are used in traffic signals to stop the vehicles?
A wire is broken in four equal parts. A packet is formed by keeping the four wires together. The resistance of the packet in comparison to the resistance of the wire will be
|
(a) Equal |
(b) One fourth |
(c) One eight |
(d) |
Assertion : Lenz’s law violates the principle of conservation of energy.
Reason : Induced e.m.f., opposes always the change in magnetic flux responsible for its production.
|
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion. |
|
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion. |
|
(c) If assertion is true but reason is false. |
|
(d) If assertion is false but reason is true. |
If an electron enters a magnetic field with its velocity pointing in the same direction as the magnetic field, then
|
(a) The electron will turn to its right |
|
(b) The electron will turn to its left |
|
(c) The velocity of the electron will increase |
|
(d) The velocity of the electron will remain unchanged |
A 10 pF capacitor is connected to a 50 V battery. How much electrostatic energy is stored in the capacitor
|
(a) 1.25 |
(b) 2.5 |
(c) 3.5 |
(d) 4.5 |
The radius of the convex surface of plano-convex lens is 20 cm and the refractive index of the material of the lens is 1.5. The focal length of the lens is
|
(a) 30 cm |
(b) 50 cm |
(c) 20 cm |
(d) 40 cm |
