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

Fusion processes, like combining two deuterons to form a He nucleus are impossible at ordinary temperatures and pressure. The reasons for this can be traced to the fact ______.

1. nuclear forces have short range.
2. nuclei are positively charged.
3. the original nuclei must be completely ionized before fusion can take place.
4. the original nuclei must first break up before combining with each other.

The electric potential V as a function of distance X is shown in the figure.

The graph of the magnitude of electric field intensity E as a function of X is ______.

(i) A ray of light incident on face AB of an equilateral glass prism, shows minimum deviation of 30°. Calculate the speed of light through the prism.

(ii) Find the angle of incidence at face AB so that the emergent ray grazes along the face AC.

1. Calculate the energy and momentum of a photon in a monochromatic beam of wavelength 331.5 nm.
2. How fast should a hydrogen atom travel in order to have the same momentum as that of the photon in part (a)?

1. Calculate the frequency of a photon of energy 6.5 × 10⁻¹⁹ J.
2. Can this photon cause the emission of an electron from the surface of Cs of work function 2.14 eV? If yes, what will be the maximum kinetic energy of the photoelectron?

A conductor of 10 Ω is connected across a 6 V ideal source. The power supplied by the source to the conductor is ______.

The primary coil having N_P turns of an ideal transformer is supplied with an alternating voltage V_P. Obtain an expression for the voltage V_S induced in its secondary coil having N_S turns.

Mention two main sources of power loss in real transformers.

The large scale transmission of electrical energy over long distances is done with the use of transformers. The voltage output of the generator is stepped-up because of ______.

Two cells of emfs 1.5 V and 2.0 V,  having internal resistances 0.2 Ω and 0.3 Ω, respectively, are connected in parallel. Calculate the emf and internal resistance of the equivalent cell.

The plot of the variation of potential difference across a combination of three identical cells in series, versus current is shown below. What is the emf and internal resistance of each cell ?

A battery of emf 12 V and internal resistance 2 Ω is connected to a 4 Ω resistor as shown in the figure.

(a) Show that a voltmeter when placed across the cell and across the resistor, in turn, gives the same reading.

(b) To record the voltage and the current in the circuit, why is voltmeter placed in parallel and ammeter in series in the circuit?

Two identical cells of emf 1.5 V each joined in parallel, supply energy to an external circuit consisting of two resistances of 7 Ω each joined in parallel. A very high resistance voltmeter reads the terminal voltage of cells to be 1.4 V. Calculate the internal resistance of each cell.

Explain the basic differences between the construction and working of a telescope and a microscope

You are given three circuit elements X, Y and Z. When the element X is connected across an a.c. source of a given voltage, the current and the voltage are in the same phase. When the element Y is connected in series with X across the source, voltage is ahead of the current in phase by π/4 . But the current is ahead of the voltage in phase by π/4when Z is connected in series with X across the source. Identify the circuit elements X, Y and Z. When all the three elements are connected in series across the same source, determine the impedance of the circuit.Draw a plot of the current versus the frequency of applied source and mention the significance of this plot.

Draw a graph to show variation of capacitive-reactance with frequency in an a.c. circuit.

Distinguish between emf and terminal voltage of a cell.

Two infinitely long straight parallel wires, '1' and '2', carrying steady currents I₁ and I₂ in the same direction are separated by a distance d. Obtain the expression for the magnetic field `vecB`due to the wire '1' acting on wire '2'. Hence find out, with the help of a suitable diagram, the magnitude and direction of this force per unit length on wire '2' due to wire '1'. How does the nature of this force changes if the currents are in opposite direction? Use this expression to define the S.I. unit of current.

A giant refracting telescope has an objective lens of focal length 15 m. If an eye piece of focal length 1.0 cm is used, what is the angular magnification of the telescope ?

If this telescope is used to view the moon, what is the diameter of the image of the moon formed by the objective lens ? the diameter of the moon is 3.48 × 10⁶ m and the radius of lunar orbit is 3.8 × 10⁸m.