# CBSE [All India]-Set-1-2010

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• Q1

Name the physical quantity whose S.I. unit is JC-1. Is it a scalar or a vector quantity?

Marks:1

Since [Potential (V)=Work done (W)/Charge (q)], the physical quantity whose S.I. unit is JC-1 is electrostatic potential. It is a scalar quantity.

• Q2

A converging lens is kept coaxially in contact with a diverging lens – both the lenses being of equal focal lengths. What is the focal length of the combination?

Marks:1

• Q3

Define self-inductance of a coil. Write its S.I. units.

Marks:1

Self inductance of a coil is defined as the induced e.m.f. produced in the coil through which the rate of change of current is unity. Its S.I. unit is henry (denoted by H).

• Q4

Two conducting wires X and Y of same diameter but different material are joined in series across a battery. If the number density of electron in X is twice that in Y, find the ratio of drift velocity of electrons in the two wires.

Marks:1

• Q5

When light travels a rarer to a denser medium, the speed decreases. Does this decrease in speed imply a decrease in the energy carried by the light wave? Justify your answer.

Marks:1

The frequency of light wave remains unchanged on travelling from one medium to another. The energy associated with light wave of frequency is , where h is the Planck’s constant. Therefore, the decrease in speed does not imply a decrease in the energy carried by the light wave on travelling from rarer medium to denser medium.

• Q6

A beam of  projected along + x-axis experiences a force due to a magnetic field along + y-axis. What is the direction of the magnetic field?

Marks:1

Therefore, according to Right Hand Rule, the magnetic field is directed along the -z-direction.

• Q7

Define ionisation energy. What is its value for a hydrogen atom?

Marks:1

The minimum energy required to knock an electron (from its ground state) completely out of an atom is known as ionisation energy. For, hydrogen atom, it is 13.6 eV.

• Q8

Name the part of electromagnetic spectrum whose wavelength lies in the range of 10-10 m. Give its one use.

Marks:1

The wavelength of X-rays is of the order of 10-10 m. X-rays are used as a diagnostic tool in medicine and as a treatment for certain forms of cancer.

• Q9

Draw a plot of the binding energy per nucleon as a function of mass number for a large number of nuclei, 2  A   240. How do you explain the constancy of binding energy per nucleon in the range 30 < A< 170 using the property that nuclear force is short-ranged?

Marks:2

A plot of the binding energy per nucleon as a function of mass number for a large number of nuclei, 2  A  240 is given below.

The constancy of the binding energy in the range 30 < A< 170 is because of the fact that the nuclear force is short ranged. A nucleon inside a nucleus will be under the influence of only some of its neighbours, which come within the range of nuclear force. The binding energy of a nucleon is proportional to the maximum number of neighbouring nucleons within the range of nuclear force. If we increase A by adding nucleons, they will not change the B.E. of a nucleon inside. Since most of the nucleons in a large nucleus (in the range of 30 < A< 170) reside inside it and not on the surface, the change in the binding energy would be small.

• Q10

Show that the electric field at the surface of a charged conductor is given by , where is the surface charge density and is a unit vector normal to the surface in the outward direction. the infinitesimal plane sheet and is directed outward direction.

Marks:2