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6.

A screw gauge with a pitch of 0.5 mm and a circular scale with 50 divisions is used to measure the thickness of a thin sheet of Aluminium. Before starting the measurement. it is found that when the two jaws of the screw gauge are brought in contact, the 45th division coincides with the main scale line and that the zero of the main scale is barely visible. What is the thickness of the sheet, if the main scale reading is 0.5mm and the 25th division coincides with the main scale line?


A) 0.75mm

B) 0.80mm

C) 0.70 mm

D) 0.50mm



7.

Choose the correct statement


A) In amplitude modulation, the amplitude of the high-frequency carrier wave is made to vary in proportional to the amplitude of the audio signal.

B) In amplitude modulation, the frequency of the high-frequency carrier wave is made to vary in proportion to the amplitude of the audio signal.

C) In frequency modulation, the amplitude of the high-frequency carrier wave is made to vary in proportion to the amplitude of the audio signal.

D) In frequency modulation, the amplitude of the high-frequency carrier wave is made to vary in proportion to the frequency of the audio signal.



8.

Half-lives of two radioactive elements A and b are 20 min and 40min respectively. Initially, the samples have an equal number of nuclei. After 80min. the ratio of decayed number of A and B nuclei will be


A) 1:16

B) 4:1

C) 1:4

D) 5:4



9.

The box of a pinhole camera of length L has a hole of radius a. I t is assumed that when the hole is illuminated by a parallel beam of light of wavelength λ the spread of the spot (obtained on the opposite wall of the camera) is the sum of its geometrical spread and the spread due to diffraction. The spot would then have its minimum size (say bmin) when


A) $a=\frac{\lambda^{2}}{L}$ and $b_{min}=(\frac{2\lambda^{2}}{L})$

B) $a=\sqrt{\lambda L}$ and $b_{min}=(\frac{2\lambda^{2}}{L})$

C) $a=\sqrt{\lambda L}$ and $b_{min}=\sqrt{4\lambda L}$

D) $a=\frac{\lambda^{2}}{L}$ and $b_{min}=\sqrt{4\lambda L}$



10.

An observer looks at a distant tree of height 10 m with a telescope of magnifying power of 20. To the observer the tree appears


A) 10 times taller

B) 10 times nearer

C) 20 times taller

D) 20 times nearer



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