## Monday, April 14, 2008

### Some JEE 2008 Questions - Paper I

1. Figure shows three resistor configurations R1, R2 and R3 connected to 3V battery. If the power dissipated
by the configuration R1, R2 and R3 is P1, P2 and P3, respectively, then
Figure : not included

(A) P1 > P2 > P3 (B) P1 > P3 > P2
(B) P2 > P1 > P3 (D) P3 > P2 > P1.

Resistances and power

Principle involved

P = V square/R equivalent

2. Which one of the following statement is WRONG in the context of X–rays generated from X–ray tube ?
(A) wavelength of characteristic X–rays decreases when the atomic number of the target increases
(B) cut–off wavelength of the continuous X–rays depends on the atomic number of the target
(C) intensity of the characteristic X–rays depends on the electrical power given to the X–ray tube
(D) cut–off wavelength of the continuous X–rays depends on the energy of the electrons in the X–ray tube.

3. Two beams of red and violet colours are made to pass separately through a prism (angle of the prism is 60º).
In the position of minimum deviation, the angle of refraction will be
(A) 30º for both the colours (B) greater for the violet colour
(C) greater for the red colour (D) equal but not 30º for both the colours.

4. An ideal gas is expanding such that PT^2
= constant. The coefficient of volume expansion of the gas is
(A)1/T

(B)2/T

(C) 3/T

(D) 4/T

1. In a Young’s double slit experiment, the separation between the two slits is d and the wavelength of the
light is λ. The intensity of light falling on slit 1 is four times the intensity of light falling on slit 2. Choose
the correct choice(s),
(A) if d = λ, the screen will contain only one maximum
(B) if λ< d < 2λ, at least one more maximum (besides the central maximum) will be observed on the screen
(C) if the intensity of light falling on slit 1 is reduced so that it becomes equal to that of slit 2, the
intensities of the observed dark and bright fringes will increase
(D) if the intensity of light falling on slit 2 is reduced so that it becomes equal to that of slit 1, the intensities of the observed dark and bright fringes will increase.

Assertion reason type

1. STATEMENT – 1
Two cylinders, one hollow (metal) and the other solid (wood) with the same mass and identical dimensions
are simultaneously allowed to roll without slipping down an inclined plane from the same height. The
hollow cylinder will reach the bottom of the inclined plane first.
and
STATEMENT – 2
By the principle of conservation of energy, the total kinetic energies of both the cylinders are identical when
they reach the bottom of the incline.
(A) Statement – 1 is True, Statement – 2 is True; Statement – 2 is a correct explanation for Statement – 1.
(B) Statement – 1 is True, Statement – 2 is True; Statement – 2 is NOT a correct explanation for
Statement– 1.
(C) Statement – 1 is True, Statement – 2 is False.
(D) Statement – 1 is False, Statement – 2 is True.

2. STATEMENT – 1
The stream of water flowing at high speed from a garden hose pipe tends to spread like a fountain when
held vertically up, but tends to narrow down when held vertically down.
and
STATEMENT – 2
In any steady flow of an incompressible fluid, the volume flow rate of the fluid remains constant.
(A) Statement – 1 is True, Statement – 2 is True; Statement – 2 is a correct explanation for Statement – 1.
(B) Statement – 1 is True, Statement – 2 is True; Statement – 2 is NOT a correct explanation for
Statement– 1.
(C) Statement – 1 is True, Statement – 2 is False.
(D) Statement – 1 is False, Statement – 2 is True.

3. STATEMENT – 1
In a Meter Bridge experiment, null point for an unknown resistance is measured. Now, the unknown
resistance is put inside an enclosure maintained at a higher temperature. The null point can be obtained at
the same point as before by decreasing the value of the standard resistance.
and
STATEMENT – 2
Resistance of a metal increases with increase in temperature.
(A) Statement – 1 is True, Statement – 2 is True; Statement – 2 is a correct explanation for Statement – 1.
(B) Statement – 1 is True, Statement – 2 is True; Statement – 2 is NOT a correct explanation for
Statement– 1.
(C) Statement – 1 is True, Statement – 2 is False.
(D) Statement – 1 is False, Statement – 2 is True.

4. STATEMENT – 1
An astronaut in an orbiting space station above the Earth experiences weightlessness.
and
STATEMENT – 2
An object moving around the Earth under the influence of Earth’s gravitational force is in a state of free–
fall.
(A) Statement – 1 is True, Statement – 2 is True; Statement – 2 is a correct explanation for Statement – 1.
(B) Statement – 1 is True, Statement – 2 is True; Statement – 2 is NOT a correct explanation for
Statement– 1.
(C) Statement – 1 is True, Statement – 2 is False.
(D) Statement – 1 is False, Statement – 2 is True.

In a mixture of H – He+ gas (He+ is singly ionized He atom), H atoms and He
+ ions are excited to their respective first excited states. Subsequently, H atoms transfer their total excitation energy to He+ ions (by collisions). Assume that the Bohr model of atom is exactly valid.

1. The quantum number n of the state finally populated in He+ ions is
(A) 2 (B) 3
(C) 4 (D) 5.

2. 45. The wavelength of light emitted in the visible region by He+ ions after collisions with H atoms is
(A) 6.5 × 10^–7 m
(B) 5.6 × 10^–7 m
(C) 4.8 × 10^–7 m
(D) 4.0 × 10^–7 m.

3. The ratio of the kinetic energy of the n = 2 electron for the H atom to that of He+ ion is

(A)1/4
(B) 1/2
(C) 1
(D) 2.
.