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NEET Physics Solved Question Paper 2010

Multiple Choice Questions

21.
A uniform wire of resistance R and length L is cut into four equal parts, each of length L/4, which are then connected in parallel combination. The effective resistance of the combination will be

R

4 R

$\frac{R}{4}$

$\frac{R}{16}$

$\frac{R}{16}$

According to ohm's law

R = $\frac{ρ l}{A}$

ρ is a constant of proportionality and depends on the material of a conductor but not on its dimensions. ρ is called resistivity

R ∝ l

i.e resistance is proportional to length

∴ $\frac{R_{1}}{R_{2}} = \frac{l_{1}}{l_{2}}$

$= \frac{L}{\frac{L}{4}}$

= 4

$R_{2} = \frac{R}{4}$ ....( $∵$ R₁ = R )

In parallel combination of such four resistances

$\frac{1}{R'} = \frac{1}{R_{2}} + \frac{1}{R_{2}} + \frac{1}{R_{2}} + \frac{1}{R_{2}}$

⇒ $\frac{1}{R'} = \frac{1}{\frac{R}{4}} + \frac{1}{\frac{R}{4}} + \frac{1}{\frac{R}{4}} + \frac{1}{\frac{R}{4}}$

⇒ $\frac{1}{R'} = \frac{4}{R} + \frac{4}{R} + \frac{4}{R} + \frac{4}{R}$

⇒ $\frac{1}{R'} = \frac{16}{R}$

⇒ $R' = \frac{R}{16}$

22.

A capacitor of capacitance 5µF is connected as shown in the figure. The internal resistance of the cell is 0.5 Ω . The amount of charge on the capacitor plates is

80 μC
40 μC
20 μC
10 μC

23.

The equivalent resistance across A and B is

2 Ω
3 Ω
4 Ω
5 Ω

24.

An electric current passes through a long straight copper wire. At a distance 5 cm from the straight wire, the magnetic field is B. The magnetic field at 20 cm from the straight wire would be

$\frac{B}{6}$
$\frac{B}{4}$
$\frac{B}{3}$
$\frac{B}{2}$

25.

An electron of mass m and charge q is travelling with a speed v along a circular path of radius r at right angles to a uniform magnetic field B. If speed of the electron is doubled and the magnetic field is halved, then resulting path would have a radius of

$\frac{r}{4}$
$\frac{r}{2}$
2r
4r

26.

A galvanometer acting as a voltmeter should have

low resistance in series with its coil
low resistance in parallel with its coil
high resistance in series with its coil
high resistance in parallel with its coil

27.

A frog can be levitated in magnetic field produced by a current in a vertical solenoid placed below the frog. This is possible because the body of the frog behaves as

paramagnetic
diamagnetic
ferromagnetic
anti-ferromagnetic

28.

The magnetic flux linked with a coil at any instant t is given by the equation $ϕ = 5 t^{3} - 100 t + 300$ . The magitude of emf induced in coil after 3 s is