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JEE Physics Solved Question Paper 2008

Multiple Choice Questions

41.

Three charges Q₀, -q and -q are placed at the vertices of an isosceles right angle triangle as in the figure. The net electrostatic potential energy is zero if Q₀ is equal to

$\frac{q}{4}$
$\frac{2 q}{\sqrt{32}}$
$\sqrt{2 q}$
+ q

42.

In the figure shown below, the terminal voltage across E₂ is

12 V
12.66 V
11.34 V
11.66 V

43.

The drift velocity of the electrons in a copper wire of length 2 m under the application of a potential difference of 220 V is 0.5 ms^-1. Their mobility (in m²V^-1s^-1)

2.5 × 10^-3
2.5 × 10^-2
5 × 10²
5 × 10^-3

44.

When two resistances R₁ and R₂ are connected in series, they consume 12 W power. When they are connected in parallel, they consume 50 W power. What the ratio of the powers of R₁ and R₂ ?

45.

In the circuit shown, if the resistance 5 Ω develops a heat of 42 J per second, heat developed in 2 Ω must be about (in Js^-1)

46.

When a Daniel cell is connected in the secondary circuit of a potentiometer, the balancing length is found to be 540 cm. If the balancing length becomes 500 cm when the cell is short circuited with 1 Ω, the internal of the cell is

0.08 Ω
0.04 Ω
1.0 Ω
1.08 Ω

47.
Two particles of equal charges after being accelerated through the same potential difference enter a uniform transverse magnetic field and describe circular path of radii R₁ and R₂ respectively. Then the ratio of their masses (M₁/M₂)
(M,/M,) i

$\frac{R_{1}}{R_{2}}$

${(\frac{R_{1}}{R_{2}})}^{2}$

$\frac{R_{2}}{R_{1}}$

${(\frac{R_{2}}{R_{1}})}^{2}$

${(\frac{R_{1}}{R_{2}})}^{2}$

Radius of circular path,

$R = \frac{mv}{qB} but mv = \sqrt{2 mqV} ∴ R = \frac{\sqrt{2 mqV}}{qB} or R \propto \sqrt{m} or \frac{{R_{1}}^{2}}{{R_{2}}^{2}} = \frac{M_{1}}{M_{2}} or \frac{M_{1}}{M_{2}} = \frac{{R_{1}}^{2}}{{R_{2}}^{2}} = {(\frac{R_{1}}{R_{2}})}^{2}$

48.

Electromagnets are made of soft iron because soft iron has

low susceptibility and low retentivity
low susceptibility and high retentivity
high permeability and low retentivity
high permeability and high coercivity

49.

Which one of the following characteristics is not associated with a ferromagnetic material ?

It is strongly attracted by a magnet
It tends to move from a region of strong magnetic field to a region of low magnetic field
Its origin is the spin of electrons
Above the Curie temperature, it exhibits paramagnetic properties

50.

The oscillating frequency of a cyclotron is 10 MHz. If the radius of its dees is 0.5 m, the kinetic energy of a proton, which is accelerated by the cyclotron is