Physics (Theory) Set 1 2015-2016 ISC (Commerce) Class 12 Question Paper Solution

In Figure 1 below, a charge Q is fixed. Another charge q is moved along a circular arc MN of radius r around it, from the point M to the point N such that the length of the arc MN = l. The work done in this process is: 

figure 1

zero 

`1/(4piε_0).(Qq)/r^2l`

`(Qq)/(2ε_0r^2)l`

`(Qq)/(2piε_0r^2)`

A carbon resistor has coloured bands as shown in Figure 2 below. The resistance of the resistor is: 

figure 2

260 ± 10% 

260 ± 5% 

2600 ± 5% 

2600 ± 10% 

A solenoid L and a resistor R are connected in series to a battery, through a switch. When the switch is put on, current I flowing through it varies with time t as shown in which of the graphs given below: 

Two thin lenses having optical powers of -10D and+ 6D are placed in contact with each other. The focal length of the combination is: 

+ 0·25 cm 

- 0·25 cm 

+ 0·25 m 

- 0·25 m 

The total energy of an electron in the ground state of the hydrogen atom is -13·6 eV. Its total energy, when a hydrogen atom is in the first excited state, is ______.

+ 13·6 eV 

+ 3·4 eV 

−3·4 eV 

−54·4 eV 

A charged oil drop weighing 1.6 x 10^-15 N is found to remain suspended in a uniform electric field of intensity 2 x 10³ Nc^-1. Find the charge on the drop. 

For a metallic conductor, what is the relation between current density (J), conductivity (σ) and electric field intensity (E)?

In Figure 3 given below, find the value of resistance x for which points A and B are at the same potential:

figure 3

Write the expression for the Lorentz force F in vector form.

A coil has a self-inductance of 0·05 Henry. Find the magnitude of the emf induced in it when the current flowing through it is changing at the rate of 100 As^-1.

To which regions of the electromagnetic spectrum do the following wavelengths belong: 
(a) 250 nm 
(b) 1500 nm 

What is the difference between polarised light and unpolarised light? 

Name the principle on the basis of which optical fibres work.

Calculate dispersive power of a transparent material given : n_v = 1.56, n_r = 1.54, n_y = 1.55. 

What is meant by short-sightedness ?

Two metals A and B have work functions 4 eV and 6 eV respectively. Which metal has a lower threshold wavelength for photoelectric effect?

Calculate angular momentum of an electron in the third Bohr orbit of a hydrogen atom.

In a nuclear reactor, what is the function of a moderator?

In our Nature, where is the nuclear fusion reaction taking place continuously?

What is the use of Zener diode?

Two-point charges Q₁ = 400 μC and Q₂ = 100 μC are kept fixed, 60 cm apart in a vacuum. Find the intensity of the electric field at the midpoint of the line joining Q₁ and Q₂.  

State Gauss’Law.

In an electric dipole, at which point is the electric potential zero ? 

Obtain an expression for equivalent capacitance when three capacitors C₁, C₂ and C₃ are connected in series.

A metallic wire has a resistance of 3.0 Ω at 0°C and 4.8 Ω at 150°C. Find the temperature coefficient of resistance of its material.

In the circuit shown in the figure below, E₁ and E₂ are two cells having emfs 2 V and 3 V respectively, and negligible internal resistance. Applying Kirchhoff’s laws of electrical networks, find the values of currents l₁ and I₂.

State how a moving coil galvanometer can be converted into an ammeter.

Draw a labelled circuit diagram of a potentiometer to measure the internal resistance ‘r’ of a cell. Write the working formula (derivation is not required). 

Define Curie temperature.

If magnetic susceptibility of a certain magnetic material is 0 0001, find its relative permeability.

Two infinitely long current carrying conductors X and Y are kept parallel to each other, 24 cm apart in a vacuum. They carry currents of 5A and 7A respectively, in the same direction, as shown in the figure below. Find the position of a neutral point, i.e., a point where resultant magnetic flux density is zero. (Ignore earth’s magnetic field). 

If current through the conductor Y is reversed in direction, will neutral point lie between X and Y, to the left of X or to the right of Y ?

Define Ampere in terms of force between two current carrying conductors.

What is the ideal transformer? 

A coil having self-inductance of 0.7 H and resistance of 165 Ω is connected to an a.c. source of 

275V,50Hz. If π = `22/7`

Calculate:
(i) Reactance of the coil
(ii) Impedance of the coil ‘
(iii) Current flowing through the coil 

Draw a labelled graph showing a variation of impedance of a series LCR circuit with frequency of the a.c. supply.

Derive Snell’s law of refraction using Huygens’s wave theory.

Monochromatic light of wavelength 650 nm falls normally on a slit of width 1.3 x 10^-4 cm and the resulting Fraunhofer diffraction is obtained on a screen. Find the angular width of the . central maxima.

In Young’s double-slit experiment, show that: 

`beta = (lambda "D")/"d"` where the terms have their usual meaning.

A ray of ordinary light is travelling in air. It is incident on air glass pair at a polarising angle of 56°. Find the angle of refraction in glass.

Find the angle of incidence at which a ray of monochromatic light should be incident on the first surface AB of a regular glass prism ABC so that the emergent ray grazes the adjacent surface AC. (Refractive Index of glass = 1 .56)

State how the focal length of a glass lens (Refractive Index 1.5) changes when it is completely immersed in: 

(i) Water (Refractive Index 1.33)
(ii) A liquid (Refractive Index 1.65)

A convex lens of a focal length 5 cm is used as a simple microscope. Where should an object be placed so that the image formed by it lies at the least distance of distinct vision (D = 25 cm)?

Draw a labelled ray diagram showing the formation of an image by a refracting telescope when the final image lies at infinity.

Monochromatic fight of wavelength 198 nm is incident on the surface of a metallic cathode whose work function is 2.5 eV How much potential difference must be applied between the cathode and the anode of a photocell to just stop the photocurrent from flowing? 

State de Broglie hypothesis

What conclusion can be drawn from Davisson and Germer’s experiment ?

How are various lines of Lyman series formed? Explain on the basis of Bohr’s theory.

Calculate the shortest wavelength of electromagnetic radiation present in Balmer series of hydrogen spectrum.

State the effect of the following changes on the X-rays emitted by Coolidge X-ray tube : 

(i) High voltage between cathode and anode is increased.
(ii) Filament temperature is increased.

Half-life of a certain radioactive material is 8 hours.

Find the disintegration constant of this material.

Half life of a certain radioactive material is 8 hours.
If one starts with 600 g of this substance, how much of it will disintegrate in one day? 

Sketch a graph showing the variation of binding energy per nucleon of a nucleus with its mass number. 

Draw a circuit diagram for the common emitter transistor amplifier. What is meant by phase reversal?

Write the truth table of the following circuit. Name the gate represented by this circuit.