Atoms — Physics STD 12 Science — Question

In a concave mirror experiment, an object is placed at a distance  from the focus and the image is formed at a distance   from the focus. The focal length of the mirror would be

(a)

(b)

(c)

(d)

The approximate ratio of resistances in the forward and reverse bias of the PN-junction diode is

(a)

(b)

(c)

(d)

Two wires have resistance of 2W and 4W connected to same voltage, ratio of heat dissipated at resistance is

(a) 1 : 2

(b) 4 : 3

(c) 2 : 1

(d) 5 : 2

Two long parallel wires P and Q are both perpendicular to the plane of the paper with distance 5 m between them. If P and Q carry current of 2.5 amp and 5 amp respectively in the same direction, then the magnetic field at a point half way between the wires is

(a)

(b)

(c)

(d)

A closed cubical box is completely filled with water and is accelerated horizontally towards right with an acceleration α. The resultant normal force by the water on the top of the box.

1. Passes through the centre of the top.
2. Passes through a point to the right of the centre.
3. Passes through a point to the left of the centre.
4. Pecomes zeros.

When we see an object, the image formed on the retina is:

1. Real.
2. Virtual.
3. Erect.
4. Inverted.

If  and  are respectively, the electric permittivity and the magnetic permeability of free space, ε and μ the corresponding quantities in a medium, the refractive index of the medium is

(a)

(b)

(c)

(d)

The plates of a parallel plate condenser are pulled apart with a velocity v. If at any instant their mutual distance of separation is d, then the magnitude of the time of rate of change of capacity depends on d as follows

(a)

(b)

(c)

(d) d

The critical angle of a medium with respect to air is 45°. The refractive index of medium is

(a) 1.41

(b) 1.2

(c) 1.5

(d) 2