Optical Instruments — Physics STD 12 Science — Question

How is the electric field at the surface of a charged conductor related to the surface charge density?

N identical spherical drops charged to the same potential V are combined to form a big drop. The potential of the new drop will be

(a) V

(b) V/N

(c) V × N

(d) V ×

If the central portion of a convex lens is wrapped in black paper as shown in the figure

(a) No image will be formed by the remaining portion of the lens

(b) The full image will be formed but it will be less bright

(c) The central portion of the image will be missing

(d) There will be two images each produced by one of the exposed portions of the lens

In the circuit shown here  and battery B = 20V. The switch  is first closed. It is then opened and afterwards   is closed. What is the charge finally on

(a) 120 μC

(b) 80 μC

(c) 40 μC

(d) 20 μC

The line of force in a magnetic field represents the direction at each point that a magnetic needle placed at the point takes up. Do they also represent the direction of the force on a moving charge at each point?

Mark the correct options:

Two slits, 4 mm apart, are illuminated by light of wavelength 6000 Å. What will be the fringe width on a screen placed 2m from the slits

(a) 0.12 mm

(b) 0.3 mm

(c) 3.0 mm

(d) 4.0 mm

Cathode rays enter into a uniform magnetic field perpendicular to the direction of the field. In the magnetic field their path will be

(a) Straight line

(b) Circle

(c) Parabolic

(d) Ellipse

This symbol represents

(a) NOT gate

(b) OR gate

(c) AND gate

(d) NOR gate