31.

In the reaction given below ${}_{86}\mathrm{A}^{222} \to {}_{84}\mathrm{B}^{210}$. How many α and β particles are emitted?

 

• 6α, 3β

• 3α, 4β

• 4α, 3β

• 3α,6β

If a convex lens of focal length 80 cm and a concave lens of focal length 50 cm are combined together, what will be their resultant power?

• +0.65 D

• -0.65 D

• +0.75 D

• -0.75 D

The phenomenon of radioactivity is :

• exothermic change which increases or decreases with  temperature

• increases on applied pressure

• nuclear process does not depend on external factors

• none of the above

The amplification factor of a triode valve is 15. If the grid voltage is changed by 0.3 V, the change in plate voltage in order to keep the current constant (in volt) is :

• 0.02

• 0.002

• 4.5

• 5.0

A plane glass slab is kept over various colour letters, the letter which appears least raised is :

• red

• violet

• green

• blue

A convex lens forms a full image of the object on a screen. If half of the lens is covered with an opaque object, then :

• the image disappears

• half of the image is seen

• full image is seen and of same intensity

• full image is seen and of decreased intensity

The time taken by light to pass through 4 mm thick glass slab of refractive index 1.5 will be : (velocity of light in air= 3 x 10⁸ m/s)

• 8 × 10^-11 s

• 2 × 10^-11 s

• 8 × 10^-8 s

• 2 × 10^-8 s

A lens acts as converging in air and diverging when immersed in water. Then, refractive index of lens is :

• equal to unity

• below 1.33

• greater than 1.33

• less than unity

A light passing through air has wavelength 6000 A^o. The wavelength when same ray passes through a glass slab of refractive index 1.5 will be:

• 2000 A^o

• 4000 A^o

• 8000 A^o

• 1200 A^o

Radius of first Bohr orbit is r. What is the radius of 2nd Bohr orbit ?

• 8 r

• 2 r

• 4 r

• $2\sqrt{2} \mathrm{r}$