Alternating Current — Physics STD 12 Science — Question

In a parabola spectrograph, the velocities of four positive ions P,Q,R and S are v₁, v₂, v₃ and v₄ respectively

(a)	(b)
(c)	(d)

If a copper rod carries a direct current, the magnetic field associated with the current will be

(a) Only inside the rod	(b) Only outside the rod
(c) Both inside and outside the rod	(d) Neither inside nor outside the rod

Take the effect of bulging of earth and its rotation in account. Consider the following statements:

1. There are points outside the earth where the value of g is equal to its value at the equator.
2. There are points outside the earth where the value of g is equal to its value at the poles.

1. Both A and B are correct.
2. A is correct but B is wrong.
3. B is correct but A is wrong.
4. Both A and B are wrong.

The introduction of a grid in a triode valve affects plate current by

(a) Making the thermionic emission easier at low temperature

(b) Releasing more electrons from the plate

(c) By increasing plate voltage

(d) By neutralising space charge

Resistance of one carbon filament and one tungsten lamp are measured individually when the lamp are lit and compared with their respective resistances when cold. Which one of the following statements will be true

(a) Resistance of the carbon filament lamp will increase but that of the tungsten will diminish when hot

(b) Resistance of the tungsten filament lamp will increase but that of carbon will diminish when hot

(c) Resistances of both the lamps will increase when hot

(d) Resistances of both the lamps will decrease when hot

AB is a potentiometer wire of length 100 cm and its resistance is 10 ohms.  It is connected in series with a resistance R = 40 ohms and a battery of e.m.f. 2 V and negligible internal resistance.  If a source of unknown e.m.f. E is balanced by 40 cm length of the potentiometer wire, the value of E is

(a) 0.8 V

(b) 1.6 V

(c) 0.08 V

(d) 0.16 V

Magnetic dipole moment of a rectangular loop is:

In a magnetic field of 0.05T, area of a coil changes from  to  without changing the resistance which is 2W. The amount of charge that flow during this period is

(a) 2.5  coulomb	(b) 2 coulomb
(c)  coulomb	(d) coulomb

In a laboratory experiment on emission from atomic hydrogen in a discharge tube, only a small number of lines are observed whereas a large number of lines are present in the hydrogen spectrum of a star. This is because in a laboratory:

1. The amount of hydrogen taken is much smaller than that present in the star.
2. The temperature of hydrogen is much smaller than that of the star.
3. The pressure of hydrogen is much smaller than that of the star.
4. The gravitational pull is much smaller than that in the star.