CBSE EXAMINATION PAPER-2024

A battery supplies 0.9 A current through a 2 Ω resistor and 0.3 A current through a 7 Ω resistor when connected one by one. The internal resistance of the battery is:

A particle of mass m and charge q describes a circular path of radius R in a magnetic field. If its mass and charge were 2m and q/2 respectively, the radius of its path would be:

A galvanometer of resistance 50 Ω is converted into a voltmeter of range (0 - 2V) using a resistor of 1.0 kΩ. If it is to be converted into a voltmeter of range (0 - 10 V), the resistance required will be:

The energy of an electron in the ground state of hydrogen atom is —13.6 eV. The kinetic and potential energy of the electron in the first excited state will be

The potential energy between two nucleons inside a nucleus is minimum at a distance of about

Assertion (A) : Equal amount of positive and negative charges are distributed uniformly on two halves of a thin circular ring as shown in figure. The resultant electric field at the centre O of the ring is along OC.

Reason (R) : It is so because the net potential at O is not zero.

Assertion (A) : The energy of a charged particle moving in a magnetic field does not change.

Reason (R) : It is because the work done by the magnetic force on the charge moving in a magnetic field is zero.

Assertion (A) : In a Young’s double-slit experiment, interference pattern is not observed when two coherent sources are infinitely close to each other.

Reason (R) : The fringe width is proportional to the separation between the two sources.

Assertion (A) : An alpha particle is moving towards a gold nucleus. The impact parameter is maximum for the scattering angle of 180°.

Reason (R) =: The impact parameter in an alpha particle scattering experiment does not depend upon the atomic number of the target nucleus.

a) Four point charges of 1 μC, -2 μC, 1 μC, and 2 μC are placed at the corners A, B, C, and D respectively, of a square of side 30 cm. Find the net force acting on a charge of 4 μC placed at the centre of the square.

a) Two energy levels of an electron in a hydrogen atom are separated by 2.55 eV. Find the wavelength of radiation emitted when the electron makes transition from the higher energy level to the lower energy level.

b) In which series of hydrogen spectrum this line shall fall?

a) Write Einstein's photoelectric equation. How did Millikan prove the validity of this equation?

b) Explain the existence of threshold frequency of incident radiation for photoelectric emission from a given surface.

a) (i) State Lenz's Law. In a closed circuit, the induced current opposes the change in magnetic flux that produced it as per the law of conservation of energy. Justify.

(ii) A metal rod of length 2 m is rotated with a frequency of 60 rev/s about an axis passing through its centre and perpendicular to its length. A uniform magnetic field of 2 T perpendicular to its plane of rotation is switched on in the region. Calculate the emf induced between the centre and the end of the rod.

a) Name the parts of the electromagnetic spectrum which are (i) also known as ‘heat waves’ and (ii) absorbed by the ozone layer in the atmosphere.

b) Write briefly one method each, of the production and detection of these radiations.

a) Explain the characteristics of a pn junction diode that makes it suitable for its use as a rectifier.

b) With the help of a circuit diagram, explain the working of a full wave rectifier.

Explain the following, giving reasons:

a) A doped semiconductor is electrically neutral.

b) In a p-n junction under equilibrium, there is no net current.

c) In a diode, the reverse current is practically not dependent on the applied voltage.

(a) (i) You are given three circuit elements X, Y and Z. They are connected one by one across a given ac source. It is found that V and I are in phase for element X. V leads I by (π/4) for element Y while I leads V by (π/4) for element Z. Identify elements X, Y and Z.

(ii) Establish the expression for impedance of circuit when elements X, Y and Z are connected in series to an ac source. Show the variation of current in the circuit with the frequency of the applied ac source.

(iii) In a series LCR circuit, obtain the conditions under which (i) impedance is minimum and (ii) wattless current flows in the circuit.