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# JEE Physics 2012 Exam Questions

#### Multiple Choice Questions

21.

Truth table for system of four NAND gates as shown in figure is

A.

280 Views

22.

In Young's double slit experiment, one of the slit is wider than other, so that the amplitude of the light from one slit is double of that from other slits. If Im be the maximum intensity, the resultant intensity I when they interfere at phase difference φ is given by

D.

Let A1 = A0, A2 = 2A0
If amplitude of resultant wave is A then

For maximum intensity

673 Views

23.

Assume that a neutron breaks into a proton and an electron. The energy released during this process is(Mass of neutron = 1.6725 x 10–27kg; mass of proton = 1.6725 x 10–27kg; mass of electron = 9 x 10–31kg)

• 0.73 MeV

• 7.10 MeV

• 6.30 MeV

• 5.4 MeV

A.

0.73 MeV

1351 Views

24.

An object 2.4 m in front of a lens forms a sharp image on a film 12 cm behind the lens. A glass plate 1cm thick, of refractive index 1.50 is interposed between lens and film with its plane faces parallel to film. At what distance (from lens) should object be shifted to be in sharp focus on film?

• 7.2 m

• 2.4 m

• 3.2 m

• 5.6 m

D.

5.6 m

Case I: u = –240cm, v = 12, by Lens formula

522 Views

25.

Proton, Deuteron and alpha particle of the same kinetic energy is moving in circular trajectories in a constant magnetic field. The radii of the proton, deuteron and alpha particle are respectively rp, rd and rα. Which one of the following relations is correct?

•  rα = rp= rd

•  rα = rp< rd

•  rα > rd> rp

•  rα = rd> rp

B.

rα = rp< rd

For charged particle moving with a speed v, in magnetic field B, on a circular track of radius

808 Views

26.

A charge Q is uniformly distributed over the surface of non conducting disc of radius R. The disc rotates about an axis perpendicular to its plane and passing through its centre with an angular velocity ω. As a result of this rotation, a magnetic field of induction B is obtained at the centre of the disc. If we keep both the amount of charge placed on the disc and its angular velocity to be constant and vary the radius of the disc than the variation of the magnetic induction at the centre of the disc will be represented by the figure

A.

Consider ring like the element of the disc of radius r and thickness dr.
If σ is charge per unit area, then charge on the element
dq = σ(2πr dr)
current ‘i’ associated with rotating charge dq is

Magnetic field dB at center due to element

So if Q and w are unchanged then

817 Views

27.

A radar has a power of 1 Kw and is operating at a frequency of 10 GHz. It is located on a mountain top of height 500 m. The maximum distance upto which it can detect object located on the surface of the earth (Radius of earth = 6.4 x 106 m) is

• 80 km

• 16 km

• 40km

• 64 km

A.

80 km

Maximum distance on earth where object can be detected is d, then

(h + R)2 = d2 + R2

⇒ d2 = h2 + 2Rh
Since, h<<R,
⇒d2 =2hR

321 Views

28.

The hydrogen atom is excited from ground state to another state with the principal quantum number equal to 4. Then the number of spectral lines in the emission spectra will be

• 2

• 3

• 3

• 4

D.

4

Number of spectral lines from a state n to ground state is

218 Views

29.

This question has statement 1 and statement 2. Of the four choices given after the statements, choose the one that best describes the two statements
Statement 1: Davisson – Germer experiment established the wave nature of electrons.
Statement 2: If electrons have wave nature, they can interfere and show diffraction.

• Statement 1 is false, Statement 2 is true

• Statement 1 is true, Statement 2 is false

• Statement 1 is true, Statement 2 is the correct explanation for statement 1

• Statement 1 is true, Statement 2 is true, Statement 2 is not the correct explanation for statement 1

C.

Statement 1 is true, Statement 2 is the correct explanation for statement 1

Davisson – Germer experiment showed that electron beams can undergo diffraction when passed through atomic crystals. This shows the wave nature of electrons as waves can exhibit interference and diffraction

155 Views

30.

A cylindrical tube, open at both ends, has a fundamental frequency, f, in the air. The tube is dipped vertically in water so that half of it is in water. The fundamental frequency of the air-column is now

• f

• f/2

• 3f/4

• 2f

A.

f

Initially for open organ pipe, fundamental frequency,

But when it is half dipped in water, then it becomes closed organ pipe of length l/2. In this case fundamental frequency.

313 Views