Semiconductor Electronics: Materials, Devices and Simple Circuits — Physics STD 12 Science — Question

A beam of monochromatic blue light of wavelength 4200Å in air travels in water (μ = 4/3). Its wavelength in water will be

(a) 2800 Å

(b) 5600 Å

(c) 3150 Å

(d) 4000 Å

Laser beams are used to measure long distance because

(a) They are monochromatic	(b) They are highly polarised
(c) They are coherent	(d) They have high degree of parallelism

The variation of decay rate of two radioactive samples A and B with time is shown in Fig. Which of the following statements are true?

Find the true statement.

Two insulated metallic spheres of 3 μF  and 5 μF capacitances are charged to 300 V and 500V respectively. The energy loss, when they are connected by a wire is

(a) 0.012 J

(b) 0.0218 J

(c) 0.0375 J

(d) 3.75 J

Which of the following is a mechanical wave?

1. Radio waves.
2. X-rays.
3. Light waves.
4. Sound waves.

A coil and a bulb are connected in series with a dc source, a soft iron core is then inserted in the coil. Then

(a) Intensity of the bulb remains the same	(b) Intensity of the bulb decreases
(c) Intensity of the bulb increases	(d) The bulb ceases to glow

Which of the following is dependent on the intensity of incident radiation in a photoelectric experiment

(a) Work function of the surface

(b) Amount of photoelectric current

(c) Stopping potential will be reduced

(d) Maximum kinetic energy of photoelectrons

A charged ball B hangs from a silk thread S, which makes an angle θ with a large charged conducting sheet  P, as shown in the figure. The surface charge density σ  of the sheet is proportional to

(a) sin θ

(b) tan θ

(c) cos θ

(c) cos θ