Magnetism And Matter — Physics STD 12 Science — Question

The decay constant of a radioactive element is 1.5   per second. Its mean life in seconds will be

(a) 1.5

(b) 4.62

(c) 6.67

(d) 10.35

A cell of internal resistance r is connected to an external resistance R. The current will be maximum in R, if

(a) R = r

(b) R < r

(c) R > r

(d) R = r/2

Hubble showed that the universe as a whole is expanding and the distant stars are receding from us. The spectral line from a star, when compared with the corresponding line from an source will then show

(a) A shift in frequency towards the red end

(b) A shift in frequency towards the violet end

(c) No shift in frequency at all

(d) A shift in frequency towards the violet end as well as a decrease in intensity

 In this reaction how many α  and β  particles are emitted

(a) 6α,3β

(b) 3 α, 4β

(c) 4 α, 3β

(d) 3α, 6β

For a cell of e.m.f. 2V, a balance is obtained for 50 cm of the potentiometer wire. If the cell is shunted by a  2Ω resistor and the balance is obtained across 40 cm of the wire, then the internal resistance of the cell is

(a) 0.25 Ω

(b) 0.50 Ω

(c) 0.80 Ω

(d) 1.00 Ω

In the middle of the depletion layer of a reverse-biased PN junction, the

(a) Potential is zero	(b) Electric field is zero
(c) Potential is maximum	(d) Electric field is maximum

The resolving power of human eye is:

The phenomenon of production of magnetic field on passing an electric current in a straight conducting wire is based on the law of:

The Young's experiment is performed with the lights of blue (λ = 4360 Å) and green colour (λ = 5460 Å), If the distance of the 4th fringe from the centre is x, then

(a) x (Blue) = x (Green)

(b) x (Blue) > x (Green)

(c) x (Blue) < x (Green)

(d)

There is a current of 20 amperes in a copper wire of  square metre area of cross-section. If the number of free electrons per cubic metre is , then the drift velocity is

(a) 125

(b) 12.5

(c) 1.25

(d) 1.25