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NEET Physics Solved Question Paper 2017

Multiple Choice Questions

21.

Two bodies A and B, have thermal emissivities of 0.01 and 0.81 respectively. The outer surface areas of both the bodies are same and emit the same radiated power. The wavelength λ_B , corresponding to the maximum intensity in radiation from B, is shifted from the wavelength λ_A , corresponding to the maximum intensity in radiation from A, by 1 µm. If the temperature of A is 5802 k, then the temperature and wavelength λ_B of body B are

1934 K, 3.5 µm
1934 K, 1.5 µm
1728 K, 32 µm
1764 K, 1.8 µm

22.

The equation of a simple harmonic wave is given by y = 3sin $\frac{π}{2}$ (50 t - x) where, x and y are in meters and t in seconds. The ratio of maximum particle velocity to the wave velocity is

2 $π$
$\frac{3}{2} π$
$3 π$
$\frac{2}{3} π$

23.

Two strings with mass per unit length of 9 gcm^-1 and 25 gcm^-1 are joined together in series. The reflection coefficient for the vibration waves are

$\frac{9}{25}$
$\frac{3}{5}$
$\frac{1}{16}$
$\frac{9}{16}$

24.

An ideal heat engine exhausting heat at 27° C is to have 25% efficiency. It must take heat at

127 °C
227° C
327° C
None of these

25.

A magnet is made to oscillate with a particular frequency, passing through a coil as shown in the figure. The time variation of the magnitude of emf generated across the coil during one cycle is

26.
Two spherical soap bubbles of radii r₁ and r₂ in vacuum combine under isothermal conditions. The resulting bubble has a radius equal to

$\frac{r_{1} + r_{2}}{2}$

$\frac{r_{1} r_{2}}{r_{1} + r_{2}}$

$\sqrt{r_{1} r_{2}}$

$\sqrt{{r_{1}}^{2} + {r_{2}}^{2}}$

$\sqrt{{r_{1}}^{2} + {r_{2}}^{2}}$

Excess of pressure, inside the first bubble p₁ = $\frac{4 T}{r}$

Similarly, p₂ = $\frac{4 T}{r_{2}}$

Let the radius of the large bubble be R. Then, excess of pressure inside the large bubble, p = $\frac{4 T}{R}$

Under isothermal condition, temperature remains constant.

So, pV = p₁V₁ + p₂V₂

$\frac{4 T}{R} (\frac{4}{3} {πR}^{3}) = \frac{4 T}{r_{1}} (\frac{4}{3} {πr}_{1}^{3}) + \frac{4 T}{r_{2}} (\frac{4}{3} {πr}_{2}^{3}) R^{2} = {r_{1}}^{2} + {r_{2}}^{2} \Rightarrow R = \sqrt{{r_{1}}^{2} + {r_{2}}^{2}}$

27.

A wooden block is floating on water kept in a beaker, 40% of the block is above the water surface. Now the beaker is kept inside a lift that starts going upward with acceleration equal to $\frac{g}{2}$ . The block will then

sink
float with 10% above the water surface
float with 40% above the water surface
float with 70% above the water surface

28.

A bar magnet has a coercivity of 4 x 10³ Am^-1. It is placed inside a solenoid of length 12 cm having 60 turns in order to demagnetise it. The amount of current that should be passed through the solenoid is