51.

An isotropic point source emits light with wavelength 500 nm. The radiation power of the source is P = 10 W . Find the number of photons passing through unit area per second at a distance of 3 m from the source.

• 5.92 x 10¹⁷ / m² s

• 2.23 x 10¹⁷ / m² s

• 2.23 x 10¹⁸ /m² s

• 5.92 x 10¹⁸ /m² s

If a proton and anti-proton come close to each other and annihilate, how much energy will be released?

• 1.5 × 10^-10 J

• 3 × 10^-10 J

• 4.5 × 10^-10 J

• 2 ×  10^-10 J

A body at rest slides down a 30° inclined plane. The time taken by it to slide down is twice the time it takes when it slides down the same distance in the absence of friction. The coefficient of friction between the body and the inclined plane is

• 0.43

• 0.37

• 0.64

• 0.75

The magnification produced by a astronomical telescope for normal adjustment is 10 and the length of the telescope is 1.1 m. The magnification, when the image is formed atleast distance of distinct vision is

• 6

• 18

• 16

• 14

Angular width of central maximum in the Fraunhoffer diffraction pattern of a slit is measured. The slit is illuminated by light of wavelength 6000 A^o. When the slit is illuminated by light of another wavelength, then the angular width decreases by 30%. The same decrease in angular width of central maximum is obtained when the original apparatus is immersed in a liquid. The refractive index of the liquid will be

• 1.25

• 1.42

• 1.67

• 1.5

An energy of 68.0 eV is required to excite a hydrogen-like atom in its second Bohr energy level to third energy level the charge of nucleus is Ze. The wavelength of a radiation required to eject the electron from first orbit to infinity is

• 2.2 nm

• 2.85 nm

• 3.2 nm

• 2.5 nm

A⁷ Li target is bombarded with a proton beam current of 10^-4 A for one hour to produce ⁷Be of activity 1.8 × 10⁸ disintegrations per second. Assuming that one ⁷Be radioactive nuclei is produced by bombarding 1000 protons, its half-life is

• 0.87 × 10⁷ s

• 0.2 × 10⁷ s

• 0.67 × 10⁸ s

• 0.87 × 10⁶ s

The truth table for the following logic circuit is

• $\left|\begin{array}{ccc}\mathrm{A}& \mathrm{B}& \mathrm{Y}\\ 0& 0& 0\\ 0& 1& 1\\ 1& 0& 1\\ 1& 1& 0\end{array}\right|$

• $\left|\begin{array}{ccc}\mathrm{A}& \mathrm{B}& \mathrm{Y}\\ 0& 0& 1\\ 0& 1& 1\\ 1& 0& 1\\ 1& 1& 1\end{array}\right|$

• $\left|\begin{array}{ccc}\mathrm{A}& \mathrm{B}& \mathrm{Y}\\ 0& 0& 1\\ 0& 1& 0\\ 1& 0& 1\\ 1& 1& 0\end{array}\right|$

• $\left|\begin{array}{ccc}\mathrm{A}& \mathrm{B}& \mathrm{Y}\\ 0& 0& 1\\ 0& 1& 1\\ 1& 0& 0\\ 1& 1& 1\end{array}\right|$

The transfer ratio B of a transistor is 50. The input resistance of the transistor when used in the common emitter configuration is 2 kΩ. The peak value of the collector AC current for an AC input voltage of 0.02 V peak is

• 200 μA

• 0.01 mA

• 0.25 mA

• 500 μA

A prism of a certain angle deviates the red and blue rays by 8 and 12, respectively. Another prism of the same angle deviates the red and blue rays by 10 and 14, respectively. The prisms are small angled and made of different materials. The dispersive power of the materials of the prisms are in the ratio

• 5 : 6

• 9 : 11

• 6 : 5

• 11 : 9