Physics (Theory) Set 1 2017-2018 ISC (Commerce) Class 12 Question Paper Solution

The order of coloured rings in a carbon resistor is red, yellow, blue and silver. The resistance of the
carbon resistor is:

a) 24 x 10⁶ Ω ± 5%

b) 24 x 10⁶ Ω ± 10%

c) 34 x 10⁴ Ω ± 10%

d) 26 x 10⁴ Ω ± 5%

A circular coil carrying a current I has radius R and number of turns N. If all the three, i.e. the current
I, radius R and number of turns N are doubled, then, the magnetic field at its centre becomes:

(a) Double

(b) Half

(c) Four times

(d) One fourth

An object is kept on the principal axis of a concave mirror of focal length 10 cm. at a distance of 15
cm from its pole. The image formed by the mirror is:

(a) Virtual and magnified

(b) Virtual and diminished

(c) Real and magnified

(d) Real and diminished

Einstein's photoelectric equation is:

a) `E_"max" = hlambda - varphi_0`

b) `E_"max"= (hc)/lambda  varphi_0`

c) `E_"max" = hv + varphi_0`

d) `E_"max" = (hv)/lambda + varphi_0`

In Bohr’s model of the hydrogen atom, the radius of the first orbit of an electron is r₀ . Then, the radius of the third orbit is:

a) `r_0/9`

b) `r_0`

c) `3r_0`

d) `9r_0`

In a potentiometer experiment, balancing length is found to be 120 cm for a cell E₁ of emf 2V. What will be the balancing length for another cell E₂ of emf 1.5V? (No other changes are made in the experiment.)

How will you convert a moving coil galvanometer into a voltmeter?

A moving charged particle q travelling along the positive x-axis enters a uniform magnetic field B.
When will the force acting on q be maximum?

Why is the core of a transformer laminated?

Ordinary (i.e. unpolarized) light is incident on the surface of a transparent material at the polarising angle. If it is partly reflected and partly refracted, what is the angle between the reflected and the refracted rays?

Define coherent sources of light

Name a material which is used in making control rods in a nuclear reactor.

Define current density. Write an expression which connects current density with drift speed

A long horizontal wire P carries a current of 50A. It is rigidly fixed. Another wire Q is placed directly above and parallel to P, as shown in Figure 1 below. The weight per unit length of the wire Q is 0.025 Nm-1 and it carries a current of 25A. Find the distance 'r' of the wire Q from the wire P so that the wire Q remains at rest

Calculate force per unit length acting on the wire B due to the current flowing in the wire A.(See
Figure 2 below)

Explain Curie’s law for a paramagnetic substance.

A rectangular coil having 60 turns and area of 0.4m² is held at right angles to a uniform magnetic field of flux density 5 × 10^-5T. Calculate the magnetic flux passing through it.

What is motional emf? State any two factors on which it depends.

What is the ratio of the speed of gamma rays to that of radio waves in a vacuum?

Identify the part of the electromagnetic spectrum which is suitable for radar system used in aircraft navigation.

A biconvex lens made of glass (refractive index 1.5) has two spherical surfaces having radii 20 cm and 30 cm. Calculate its focal length.

State any two difference between the primary rainbow and secondary rainbow

State de Broglie hypothesis

With reference to the photoelectric effect, define threshold wavelength

Calculate the minimum wavelength of the spectral line present in Balmer series of hydrogen

What are means by pair annihilation? Write a balanced equation for the same.

What is meant by the terms half-life of a radioactive substance and binding energy of a nucleus?

In a communication system, what is meant by modulation?

State any two types of modulation

Obtain an expression for an intensity of electric field at a point at the end of position, i.e., the axial position of an electric dipole.

x

Deduce an expression for equivalent capacitance C when three capacitors C₁, C₂ and C₃ connected in parallel.

ε₁ and ε₂ are two batteries having emf of 34V and 10V respectively and internal resistance of 1Ω and 2Ω respectively. They are connected as shown in the figure below. Using Kirchhoff’s Laws of electrical networks, calculate the currents I₁ and I₂.

An electrical bulb is marked 200V, 100W. Calculate the electrical resistance of its filament. If five such
bulbs are connected in series to a 200V supply, how much current will flow through them?

For any prism, prove that :

'n' or `mu = sin((A + delta_m)/2)/sin(A/2)`

where the terms have their usual meaning

When two thin lenses are kept in contact, prove that their combined or effective focal length F is given by:

`1/F = 1/f_1  + 1/f_2`

where the terms have their usual meaning.

In Young’s double slit experiment, show graphically how the intensity of light varies with distance

In Fraunhofer diffraction, how is the angular width of the central bright fringe affected when slit separation is increased?

Write one balanced equation to show Nuclear fission

Write one balanced equation to show Nuclear fusion

With reference to semiconductor devices, define a p-type semiconductor and a Zener diode.

What is the use of Zener diode?

An alternating emf of 220 V is applied to a circuit containing a resistor R having the resistance of 160Ω and a capacitor ‘C’ is series. The current is found to lead the supply voltage by an angle

`θ = tan^(-1) ("3/4")`

a) Calculate

1) The capacitive reactance

2) The impedance of the circuit

3) Current flowing in the circuit

b) If the frequency of the applied emf is 50 Hz, what is the value of the capacitance of the capacitor ‘C’?

An A.C. generator generating an emf of ε = 300 sin (100 πt) V is connected to a series combination of 16μ F capacitor, 1 H inductor and 100 Ω resistor.

Calculate :

1) An impedance of the circuit at the given frequency.

2) Resonant frequency `f_0`

3)Power factor at the resonant frequency `f_0`.

Draw a labelled ray diagram of an image formed by a refracting telescope with the final image formed at infinity. Derive an expression for its magnifying power with the final image at infinity

Derive Snell’s law on the basis of Huygen’s wave theory when the light is travelling from a denser to a rarer medium.

With the help of an experiment, state how will you identify whether a given beam of light is polarised or unpolarized?

The forward characteristic curve of a junction diode is shown in Figure 4 below :

Calculate the resistance of the diode at

(1) V = 0.5 V

(2) I = 60 mA

Draw separate energy band diagram for conductors, semiconductors and insulators and
label each of them.

The arrangement given below represents a logic gate :

Copy the following truth table in your answer booklet and complete it showing outputs at C
and D.

Draw a labelled diagram of a common emitter amplifier, showing waveforms of the signal voltage and output voltage.