Nuclei — Physics STD 12 Science — Question

Which of the following is not a correct statement

(a) Resistivity of electrolytes decreases on increasing temperature

(b) Resistance of mercury falls on decreasing its temperature

(c) When joined in series a 40 W bulb glows more than a 60 W bulb

(d) Resistance of 40 W bulb is less than the resistance of 60 W bulb

In the given figure, a current of constant magnitude is flowing in the wire AB. Direction of induced current flowing through the wire is:

Two atoms of the same element are found to have different number of neutrons in their nuclei. These two atoms are:

Assertion :   The tangent galvanometer can be made more sensitive by increasing the number of turns of its coil.

Reason    : Current through galvanometer is proportional to the number of turns of coil.

(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.

A sample of radioactive element has a mass of 10 gm at an instant t = 0.The approximate mass of this element in the sample after two mean lives is

(a) 2.50 gm

(b) 3.70 gm

(c) 6.30 gm

(d) 1.35 gm

If  is the original mass of the substance of half life period   years, then the amount of substance left after 15 years is

(a)

(b)

(c)

(d)

A horizontal loop abcd is moved across the pole pieces of a magnet as shown in fig. with a constant speed v. When the edge ab of the loop enters the pole pieces at time t = 0 sec. Which one of the following graphs represents correctly the induced emf in the coil

(a)

(b)

(c)

(d)

A magnetic dipole is acted upon by two magnetic fields which are inclined to each other at an angle of 75° One of the fields has a magnitude of 15 mT. The dipole attains stable equilibrium at an angle of 30° with this field. The magntidue of the other field (in mT) is close to:

The axis of rotation of a purely rotating body:

1. Must pass through the centre of mass.
2. May pass through the centre of mass.
3. Must pass through a particle of the body.
4. May pass through a particle of the body.

The size of an object as perceived by an eye depends primarily on:

1. Actual size of the object.
2. Distance of the object from the eye.
3. Aperture of the pupil.
4. Size of the image formed on the retina.