Science (English Medium) कक्षा १२ - CBSE Question Bank Solutions

Why cannot two independent monochromatic sources produce sustained interference pattern?
Deduce, with the help of Young's arrangement to produce interference pattern, an expression for the fringe width.

Given a uniform electric field \[\vec{E} = 2 \times {10}^3 \ \hat{i}\]  N/C, find the flux of this field through a square of side 20 cm, whose plane is parallel to the y−z plane. What would be the flux through the same square, if the plane makes an angle of 30° with the x−axis ?

A potentiometer wire of length 1.0 m has a resistance of 15 Ω. It is connected to a 5 V battery in series with a resistance of 5 Ω. Determine the emf of the primary cell which gives a balance point at 60 cm.

Given a uniform electric filed \[\vec{E} = 4 \times {10}^3 \ \hat{i} N/C\]. Find the flux of this field through a square of 5 cm on a side whose plane is parallel to the Y-Z plane. What would be the flux through the same square if the plane makes a 30° angle with the x-axis?

Describe briefly how the Davisson-Germer experiment demonstrated the wave nature of electrons.

A cell of emf ‘E’ and internal resistance ‘r’ draws a current ‘I’. Write the relation between terminal voltage ‘V’ in terms of E, I and r ?

Why photoelectric effect cannot be explained on the basis of wave nature of light? Give reasons.

Two charges of magnitudes −2Q and +Q are located at points (a, 0) and (4a, 0) respectively. What is the electric flux due to these charges through a sphere of radius ‘3a’ with its centre at the origin?

Two identical cells, each of emf E, having negligible internal resistance, are connected in parallel with each other across an external resistance R. What is the current through this resistance?

A rectangular conductor LMNO is placed in a uniform magnetic field of 0.5 T. The field is directed perpendicular to the plane of the conductor. When the arm MN of length of 20 cm is moved towards left with a velocity of 10 ms⁻¹, calculate the emf induced in the arm. Given the resistance of the arm to be 5 Ω (assuming that other arms are of negligible resistance) find the value of the current in the arm.

Two charges of magnitudes −3Q and + 2Q are located at points (a, 0) and (4a, 0) respectively. What is the electric flux due to these charges through a sphere of radius ‘5a’ with its centre at the origin?

Two charges of magnitudes +4Q and − Q are located at points (a, 0) and (− 3a, 0) respectively. What is the electric flux due to these charges through a sphere of radius ‘2a’ with its centre at the origin?

A parallel beam of light of 450 nm falls on a narrow slit and the resulting diffraction pattern is observed on a screen 1.5 m away. It is observed that the first minimum is at a distance of 3 mm from the centre of the screen. Calculate the width of the slit.

A cell of emf E and internal resistance r is connected to two external resistance R₁ and R₂ and a perfect ammeter. The current in the circuit is measured in four different situations:

(i) without any external resistance in the circuit

(ii) with resistance R₁ only

(iii) with R₁ and R₂ in series combination

(iv) with R₁ and R₂ in parallel combination

The currents measured in the four cases are 0.42 A, 1.05 A, 1.4 A and 4.2 A, but not necessarily in the order. Identify the currents corresponding to the four cases mentioned above.

Two cells of emf E₁, E₂ and internal resistance r₁ and r₂ respectively are connected in parallel as shown in the figure.

Deduce the expressions for

(1) the equivalent e.m.f of the combination

(2) the equivalent resistance of the combination, and

(3) the potential difference between the point A and B.

A thin straight infinitely long conducting wire having charge density λ is enclosed by a cylindrical surface of radius r and length l, its axis coinciding with the length of the wire. Find the expression for the electric flux through the surface of the cylinder.

Figure shows three point charges +2q, −q and + 3q. Two charges + 2q and −q are enclosed within a surface ‘S’. What is the electric flux due to this configuration through the surface ‘S’?

Deduce the expression for the potential energy of a system of two point charges q₁ and q₂ brought from infinity to the points `vecr_1`and `vecr_2`respectively in the presence of external electric field `vecE`.

A cell of emf ‘E’ and internal resistance ‘r’ is connected across a variable resistor ‘R’. Plot a graph showing the variation of terminal potential ‘V’ with resistance R. Predict from the graph the condition under which ‘V’ becomes equal to ‘E’.

By what percentage will the transmission ranges of TV tower be affected when the height of the tower is increased by 21%?