AGARWAL’S PHYSICS RAVI AGARWAL (M.Sc.) – 9913650950 / 9374727052TIME: 1Hr.30 min. CH.8 to 14( Numericals) Marks: 54

1 A 110V, 10W lamp has to be connected with an a.c. source of 230V and 50Hz. Calculate the inductance of the choke coil to be connected in series with it.

2 A 1000 W is kept at the centre of a spherical surface and is at a distance of 10m from the surface. Calculate the force acting on the surface of the sphere by the electromagnetic waves, alongwith Eo, Bo (the maximum electric and magnetic field strengths) and I (the intensity of the waves). Take the working efficiency of the bulb 2.5% and consider it as a point source. ∈o = 8.85 × 10-12 SI and C = 3.0 ×108 ms-1. Also calculate the energy density on the surface.

3 Diameter of the moon is 2160 miles. It is 2.21×105 miles away from a concave mirror having radius of curvature 3m. Find the diameter of the image formed in the mirror. Neglect the radius of curvature of the mirror in comparison to the distance of the moon. The mirror is placed such that it’s principal axis passes through the centre of the moon.

4 Light of wavelength 5000 is incident on a slit of width 2mm in Fraunhoffer diffraction. Find the width of 2nd maximum on the screen placed at the focal plane of the lens of focallength 100cm. The lens is placed closed to the slit.

5 Calculate the maximum wavelength of Balmer series in the hydrogen spectrum. Calculate the corresponding wave number. (Rydberg constant = 1.097 × 10-7m

6 A beam of photons of intensity 2.0W/m2 each of energy 10.6eV is incident on 1.0×10-4 m2 area of the surface having work function 5.6eV. If 0.53% of incident photons emits photo-electrons, find the number of photons emitted in 1sec. Find the minimum and maximum energy of these photo electrons.

7 11,000 W of electric power at 220V is transmitted over a cable. The resistance of the cable is equal to R. Calculate the power lost in the above case. Also calculate the loss in the transmission of the power, if the same amount of power is transmitted at 22,000 V. Which of the two options will be preferred by you?

8 In a X-ray tube the p.d. between the anode and cathode is 12.4kV and current flowing is 2mA. Find, (1) the no. of electrons striking the anode in 1s.(2) the speed of electrons while striking the anode,(3) minimum wavelength (λmin) emitted.

9 In Young’s experiment width of one slit is 3 times that of another. The intensity of light is proportional to the width of the slit, find the ratio of maximum to minimum intensity.

10 Consider the radius of a nucleus to be 10-15m. If an electron is assumed to be in such nucleus, what will be its length.

11 For a thin lens, prove that when the heights of the objects and the image are equal, object distance and image distance are equal to 2f.

12 Plane polarized light is normally incident on a Polaroid. The Polaroid is rotated with the angular speed of 10rad/s about this ray of light. If the incident light energy in one second is 4mJ, what will be the light energy emerging out of the Polaroid during one rotation?

13 Calculate the quantum no. for which the radius of the orbit of electron in Be+3 would be equal to that for the ground state of electron in a hydrogen atom. Also compare the energy of the two states.

14 Calculate the resultant inductance of two inductors L1 and L2 when they are connected in parallel.

15 Depth of a well is 5.5m and refractive index of water is 1.33. If viewed from the top by how much height would the bottom of the well appear to be shifted up?

16 An object is moving towards the concave mirror along it’s principal axis with uniform velocity vo. Prove that when the object is at distance u from the concave mirror, velocity of

the image is . R is the radius of the curvature of the mirror.

17 Two protons in a star experience head on collision. Energy of each proton is 12KeV. Find their closest distance of approach.

18 A vessel is fully filled with the liquid having refractive index 5/3. At the bottom of the vessel a point like source of light is kept. An observer looks at the source of light from the top. Now an opaque circular disc is kept on the surface of the water in such a way that its centre just rest above the light source. Now liquid is taken out of the vessel gradually. Calculate the maximum height of the liquid to be kept so that light source cannot be seen from the top. Radius of the disc is 1cm.

Failure may be in life or in exam means not having planning or

wrong planning for the given task or work.

Ravi Agarwal.