Solid targets of different elements are bombarded by highly energetic electron beams. The frequency (f) of the characteristic X-rays emitted from different targets varies with atomic number Z as

• f ∝ $\sqrt{\mathrm{Z}}$

• f ∝ Z²

• f ∝ Z

• f ∝ Z^3/2

In a semiconductor material the mobilities of electrons and holes are μ_e and  μ_n respectively. Which of the following is true?

• μ_{e >} μ_n

• μ_e < μ_n

• μ_e = μ_n

• μ_e< 0 ;  μ_n > 0

The magnetic moment ( μ) of a revolving  electron around the nucleus varies with principal quantum number n as

•  μ ∝ n

•  μ  ∝ 1/n

•  μ ∝  n²

• μ ∝ 1/n²

A radioactive material has a half-life of 10 days. What fraction of the material would remain after 30 days?

• 0.5

• 0.25

• 0.125

• 0.33

According to Hubble's law, the redshift (Z) of a receding galaxy and its distance r from earth are related as

• Z ∝ r 

• Z ∝ 1/r

• Z ∝ 1/r²

• Z ∝ r^3/2 

46.

When exposed to sunlight, thin films of oil on water often exhibit brilliant colours due to the phenomenon of

• interference

• diffraction

• dispersion

• polarisation

The voltage gain of the following amplifier is

• 10

• 100

• 1000

• 9.9

Energy required to break one bond in DNA is approximately

• ∼ 1 eV

• ∼ 0.1 eV

• ∼ 0.01 eV

• ∼ 2.1 eV

The apparent depth of water in cylindrical water tank of diameter 2R cm is reducing at the rate of  x cm/minute when water is being drained out at a constant rate. The amount of water drained in  c.c. per minute is ( n₁ = refractive index of air, n₂ = refractive index of water)

• $\frac{\mathrm{x\pi } {\mathrm{R}}^2 {\mathrm{n}}_1}{{\mathrm{n}}_2}$

• $\frac{{\mathrm{x\pi R}}^2 {\mathrm{n}}_2}{{\mathrm{n}}_1}$

• $\frac{2\mathrm{\pi R} {\mathrm{n}}_1}{{\mathrm{n}}_2}$

• $\mathrm{\pi }$R²x

Assertion: Specific gravity of a fluid is a dimensionless quantity.

Reason: It is the ratio of density of fluid to the density of water.

• If both assertion and reason are true and reason is the correct explanation of assertion

• If both assertion and reason are true but reason is not the correct explanation of assertion

• If assertion is true but reason is false

• If both assertion and reason are false