Magnetism And Matter — Physics STD 12 Science — Question

The working of optical instruments like camera, microscope, telescope, etc. having glass lenses is based on a phenomenon of light. Identify the phenomenon.

Lenz's law gives:

Two parallel wires are carrying electric currents of equal magnitude and in the same direction. They exert(a) An attractive force on each other(b) A repulsive force on each other(c) No force on each other(d) A rotational torque on each other

Assertion  :  The drift velocity of electrons in a metallic wire will decrease, if the temperature of the wire is increased.
Reason      : On increasing temperature, conductivity of metallic wire decreases.(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 the assertion and reason both are false.

When sound wave is refracted from air to water, which of the following will remain unchanged?

1. Wave number.
2. Wavelength.
3. Wave velocity.
4. Frequency.

A polariser is used to(a) Reduce intensity of light(b) Produce polarised light(c) Increase intensity of light(d) Produce unpolarised light

Which of the following statement regarding transformer is incorrect?

If the two ends of a p-n junction are joined by a wire:

1. There will not be a steady current in the circuit.
2. There will be a steady current from the n-side to the p-side.
3. There 'will a steady current from the p-side. to the n-side.
4. There may or may not be a current depending upon the resistance of the connecting wire.

An electric bulb is made to work at 12 V dc. When this bulb is joined with an ac source, it gives normal brightness. Peak voltage of ac source is:

Diode is used as a/an(a) Oscillator(b) Amplifier(c) Rectifier(d) Modulator