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# JEE Physics 2005 Exam Questions

#### Multiple Choice Questions

61.

A photocell is illuminated by a small bright source placed 1 m away. When the same source of light is placed 1 /2 m away, the number of electrons emitted by photocathode would

• decrease by a factor of 4

• increase by a factor of 4

• decrease by a factor of 2

• increase by a factor of 2

B.

increase by a factor of 4

On doubling the distance the intensity becomes one fourth i.e. only one-fourth of photons now strike the target in comparison to the previous number. Since the photoelectric effect is a one photon-one electron phenomenon, so only one-fourth photoelectrons are emitted out of the target hence reducing the current to one fourth the previous value.
225 Views

62.

The diagram shows the energy levels for an electron in a certain atom. Which transition shown represents the emission of a photon with the most energy?

• lll

• IV

• I

• II

A.

lll

270 Views

63.

Starting with a sample of pure 66Cu, 7/8 of it decays into Zn in 15 minutes. The corresponding half-life is

• 10 minutes

• 15 minutes

• 5 minutes

• 7.5 minutes

C.

5 minutes

452 Views

64.

Two point white dots are 1 mm apart on a black paper. They are viewed by eye of pupil diameter 3 mm. Approximately, what is the maximum distance at which these dots can be resolved by the eye? [ Take wavelength of light = 500 nm ]

• 5 m

• 1 m

• 6 m

• 3 m

A.

5 m

275 Views

65.

A thin glass (refractive index 1.5) lens has an optical power of – 5D in air. Its optical power in a liquid medium with refractive index 1.6 will be

• 1 D

• 5/8 D

• -1 D

• 25 D

B.

5/8 D

165 Views

66.

The electrical conductivity of a semiconductor increases when electromagnetic radiation of wavelength shorter than 2480 nm is incident on it. The band gap in (eV) for the semiconductor is

• 1.1 eV

• 2.5 eV

• 0.5 eV

• 0.7 eV

C.

0.5 eV

Eg = hc/λ

= 0.5eV

0.5 eV

284 Views

67.

If radius of  nucleus is estimated to be 3.6 Fermi then the radius nucleus

• 6 fermi

• 8 fermi

• 4 fermi

• 5 fermi

A.

6 fermi

310 Views

68.

The intensity of gamma radiation from a given source is I. On passing through 36 mm of lead, it is reduced to l/8. The thickness of lead which will reduce the intensity to l/2 will be

• 6 mm

• 9 mm

• 18 mm

• 12 mm

D.

12 mm

625 Views

69.

A Young’s double slit experiment uses a monochromatic source. The shape of the interference fringes formed on a screen is

• hyperbola

• circle

• straight line

• parabola

C.

straight line

390 Views

70.

A fish looking up through the water sees the outside world contained in a circular horizon. If the refractive index of water is 4/3 and the fish is 12 cm below the surface, the radius of this circle in cm is

B.

287 Views