Atoms — Physics STD 12 Science — Question

ABC is a right angled triangle in which AB = 3 cm  and BC = 4 cm. And Ð ABC = p/2. The three charges +15, +12  and -20 e.s.u.  are placed respectively on A, B and C. The force acting on B  is

(a) 125 dynes

(b) 35 dynes

(c) 25 dynes

(d) Zero

Diode is used as a/an

(a) Oscillator

(b) Amplifier

(c) Rectifier

(d) Modulator

In an interference experiment, the spacing between successive maxima or minima is  (Where the symbols have their usual meanings)

(a)

(b)

(c)

(d)

The refractive indices of water and glass with respect to air are 1.2 and 1.5 respectively. The refractive index of glass with respect to water is

(a) 0.6

(b) 0.8

(c) 1.25

(d) 1.75

A double star is a system of two stars rotating about their centre of mass only under their mutual gravitational attraction. Let the star have mass m and 2m and their separation be l. Their time period of rotation about their centre of mass will be proportional to

(a)

(b) l

(c)

(d)

The magnetic flux in a coil of 100 turns increases by 12 × 10³ Maxwell in 0.2 second due to the motion of a magnet. The emf induced in the coil will be.

Consider a current carrying wire (current I) in the shape of a circle. Note that as the current progresses along the wire, the direction of j (current density) changes in an exact manner, while the current I remain unaffected. The agent that is essentially responsible for is:

If the frequency of an A.C is made 4 times of its initial value, the inductive reactance will.

To obtain maximum EMF from a number of cells, they must be connected in.

There are two coils A and B as shown in Fig. A current starts flowing in B as shown, when A is moved towards B and stops when A stops moving. The current in A is counterclockwise. B is kept stationary when A moves. We can infer that: