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NEET Physics Solved Question Paper 2009

Multiple Choice Questions

21.

The potential energy of a molecule on the surface of a liquid compared to one inside the liquid is

zero
lesser
equal
greater

22.

Two spherical conductors B and C having equal radii and carrying equal charges in them repel each other with a force F when kept apart at some distance. A third spherical conductor having same radius as that of B but uncharged, is brought in contact with B, then brought in contact with C and finally removed away from both. The new force of repulsion between B and C is

$\frac{F}{4}$
$\frac{3 F}{4}$
$\frac{F}{8}$
$\frac{3 F}{8}$

23.

In gamma ray emission from a nucleus

both the neutron number and the proton number change
there is no change in the proton number and the neutron number
only the neutron number changes
only the proton number changes

24.

The resistance of an ammeter is 13 Ω and its scale is graduated for a current upto 100 A. After an additional shunt has been connected to this ammeter it becomes possible to measure currents upto 750 A by this meter. The value of
shunt resistance is

20 Ω
2 Ω
0.2 Ω
2 KΩ

25.

The primary and secondary coils of a transformer have 50 and 1500 turns respectively. If the magnetic flux $ϕ$ linked with the primary coil is given by $ϕ = ϕ_{o} + 4 t$ where $ϕ$ is weber, t is time in second and $ϕ_{o}$ is a constant, the output vltage across the secondary coil is

90 v
120 V
220 V
30 V

26.

A transformer is used to light a 100 W and 110 V lamp from a 220 V mains. If the main current is 0.5 A, the efficiency of the transformer is approximately

27.

A charged particle (charge q) is moving in a circle of radius R with uniform speed v. The associated magnetic moments given by

$\frac{q ν R}{2}$
qνR²
$\frac{q ν R^{2}}{2}$
qνR

28.

A steady current of 1.5 A flows through a copper voltameter for 10 min. If the electrochemical equivalent of copper is 30x 10^-5 g C^-1 , the mass of copper deposited on the electrode will be

0.40 g
0.50 g
0.67 g
0.27 g

29.
In a mass spectrometer used for measuring the masses of ions, the ions are initially accelerated by an electric potential V and then made to describe semicircular paths of radius R using a magnetic field B. If V and B are kept constant the ratio $(\frac{charge on the ion}{mass of the ion})$ will be proportional to

$\frac{1}{R}$

$\frac{1}{R^{2}}$

R²

R

$\frac{1}{R^{2}}$

The radius of the orbit in which ions moving is determined by the relation as given below

$\frac{{mv}^{2}}{R} = qvB$

where m is the mass, v is velocity, q is charge of ion and B is the flux density of the magnetic field, so that qvB is the magnetic force acting on the ion, and $\frac{{mv}^{2}}{R}$ is the centripetal force on the ion moving in a curved path of radius R.

The angular frequency of rotation of the ions about the vertical field B is given by

$ω = \frac{v}{R} = \frac{qB}{m} ω = 2 πv$

where ν is the frequency.

Energy of ion is given by

$E = \frac{1}{2} {mν}^{2} = \frac{1}{2} m ({Rω}^{2}) \Rightarrow E = \frac{1}{2} m R^{2} B^{2} \frac{q^{2}}{m^{2}} \Rightarrow E = \frac{1}{2} \frac{R^{2} B^{2} q^{2}}{m} . . . . (i)$

If ions are accelerated by electric potential V, then energy attained by ions

E = qV .... (ii)

from equation (i) and (ii) we get

$q V = \frac{1}{2} \frac{R^{2} B^{2} q^{2}}{m} \Rightarrow \frac{q}{m} = \frac{2 V}{R^{2} B^{2}}$

If V and B are kept constant

$\frac{q}{m} \propto \frac{1}{R^{2}}$

30.

Three resistances P, Q, R each of 2Ω and an unknown resistance S form the four arms of a Wheatstone's bridge circuit. When a resistance of 6Ω is connected in parallel to S the bridge gets balanced. What is the value of S?