Bihar Board 12th Physics Objective Questions and Answers

## Bihar Board 12th Physics VVI Objective Questions Model Set 3 in English

Question 1.

At constant potential difference, the resistance of any electric circuit is halved, the value of heat produced will be

(a) half

(b) double

(c) four times

(d) same

Answer:

(b) double

Question 2.

The power factor of L-R circuit is

(a) R + WL

(b) \(\frac{R}{\sqrt{R^{2}+W^{2} L^{2}}}\)

(c) \(\mathrm{R} \sqrt{\mathrm{R}^{2}+\mathrm{W}^{2} \mathrm{L}^{2}}\)

(d) \(\frac{\mathrm{WL}}{\mathrm{R}}\)

Answer:

(b) \(\frac{R}{\sqrt{R^{2}+W^{2} L^{2}}}\)

Question 3.

The stored energy, of a capacitor, charged to 100 V is 1 J. Capacitance of the capacitor is

(a) 2 × 10^{4} F

(b) 2 × 10^{4} F

(c) 2 × 10^{2} F

(d) 2 × 10^{-2} F

Answer:

(b) 2 × 10^{4} F

Question 4.

The current flowing in a wire is 1 A. If the charge of an electron is 1.6 × 10^{-19} C, then the number of, electrons flowing through the wire per second is

(a) 0.625 × 10^{13}

(b) 6.25 × 10^{18}

(c) 1.6 × 10^{-19}

(d) 1.6 × 10^{19}

Answer:

(b) 6.25 × 10^{18}

The half-life formula Determine the original amount of the substance.

Question 5.

The time in which radioactive substance becomes half of its initial amount is called

(a) average life

(b) half-life

(c) time – period

(d) decay constant

Answer:

(b) half-life

Question 6.

Deviation of a thin prism of refractive index n and angle of prism A is

(a) (1 – n) A

(b) (n – 1) A

(c) (n + 1) A

(d) (1 + n) A^{2}

Answer:

(b) (n – 1) A

Question 7.

Two-point charges of +10 µc and -10 µc are placed at a distance 40 cm in air. The potential energy of the system will be

(a) 2.25 J

(b) 2.35 J

(c) -2.25 J

(d) -2.35 J

Answer:

(c) -2.25 J

Question 8.

A convex lens (n = 1.5) is immersed in water (n = 1.33), then it will behave as a

(a) Converging lens

(b) Diverging lens

(c) Prism

(d) Concave mirror

Answer:

(a) Converging lens

Question 9.

The susceptibility of a paramagnetic substance is

(a) Constant

(b) Zero

(c) Infinity

(d) Depends on the magnetic field

Answer:

(a) Constant

Question 10.

The energy of a photon of wavelength λ is

(a) hcλ

(b) \(\frac{h c}{\lambda}\)

(c) \(\frac{h \lambda}{c}\)

(d) \(\frac{\lambda}{h c}\)

Answer:

(b) \(\frac{h c}{\lambda}\)

Question 11.

Light owes its colour to its

(a) frequency

(b) velocity

(c) phase

(d) amplitude

Answer:

(a) frequency

Question 12.

Power of an electric circuit is

(a) V . R

(b) V^{2} . R

(c) \(\frac{V^{2}}{R}\)

(d) V^{2} Rt

Answer:

(c) \(\frac{V^{2}}{R}\)

Question 13.

The electrric potential in equatorial position of an electric dipole is

(a) \(\frac{1}{4 \pi \varepsilon_{0}} \frac{p \cos \theta}{r^{2}}\)

(b) \(\frac{1}{4 \pi \varepsilon_{0}} \frac{p}{r^{2}}\)

(c) \(\frac{1}{4 \pi \varepsilon_{0}} \frac{p}{r}\)

(d) Zero

Answer:

(d) Zero

Question 14.

The working of the dynamo is based on the principle of

(a) Heating effect of current

(b) Electromagnetic induction

(c) Induced magnetism

(d) Induced electricity

Answer:

(b) Electromagnetic induction

Question 15.

The modulation index in amplitude modulation

(a) is always zero

(b) lies between 0 and 1

(c) lies between 1 and ∞

(d) Can never exceed 0.5

Answer:

(b) lies between 0 and 1

Question 16.

The solar spectrum is

(a) Continuous

(b) Line spectrum

(c) The spectrum of black lines

(d) The spectrum of black bands

Answer:

(a) Continuous

Question 17.

Unit of surface charge density is

(a) Coulomb/metre^{2}

(b) Newton/metre

(c) Coulomb/Volt

(d) Coulomb-metre

Answer:

(a) Coulomb/metre^{2}

Question 18.

The wavefront due to a point source at a finite distance from the source is

(a) Spherical

(b) Cylindrical

(c) Plane

(d) Circular

Answer:

(a) Spherical

Question 19.

The resistance of ideal ammeter is

(a) Zero

(b) very small

(c) very large

(d) infinite

Answer:

(a) Zero

Question 20.

When two bulbs of power 60 W and 40 W are connected in series, then the power of their combination will be

(a) 100 W

(b) 2400 W

(c) 30 W

(d) 24 W

Answer:

(d) 24 W

Question 21.

In earth’s magnetic field BH, if the frequency of oscillation of a magnetic needle is n, then

(a) n ∝ B_{H}

(b) n^{2} ∝ B_{H}

(c) n ∝ B_{H}^{2}

(d) n^{2} ∝ \(\frac{1}{\mathrm{B}_{\mathrm{H}}}\)

Answer:

(b) n^{2} ∝ B_{H}

Question 22.

The magnifying power of an astronomical telescope for normal adjustment is

(a) \(-\frac{f_{o}}{f_{e}}\)

(b) -f_{0} × f_{e}

(c) \(-\frac{f_{e}}{f_{o}}\)

(d) -f_{0} + f_{e}

Answer:

(d) -f_{0} + f_{e}

Question 23.

In a step-up transformer, no. of turns in primary and secondary coils are N_{1} and N_{2}, then

(a) N_{1} > N_{2}

(b) N_{2} > N_{1}

(c) N_{1} = N_{2}

(d) N_{1} = 0

Answer:

(b) N_{2} > N_{1}

Question 24.

The ratio of root mean square (rms) value and peak value of an alternating current is

(a) √2

(b) \(\frac{1}{\sqrt{2}}\)

(c) \(\frac{1}{2}\)

(d) 2√2

Answer:

(b) \(\frac{1}{\sqrt{2}}\)

Question 25.

Which one of the following has a maximum refractive index?

(a) glass

(b) water

(c) iron

(d) diamond

Answer:

(d) diamond

Question 26.

With the increase of temperature the resistivity of the semiconductor

(a) increases

(b) decreases

(c) remains constant

(d) becomes zero

Answer:

(b) decreases

Question 27.

Cylindrical lenses are used to correct the eye defect called

(a) myopia

(b) hypermetropia

(c) astigmatism

(d) presbyopia

Answer:

(c) astigmatism

Question 28.

The direction of propagation of electromagnetic wave is

(a) Parallel to \(\overrightarrow{\mathrm{B}}\)

(b) Parallel to \(\overrightarrow{\mathrm{E}}\)

(c) Parallel to \(\overrightarrow{\mathrm{B}} \times \overrightarrow{\mathrm{E}}\)

(d) Parallel to \(\overrightarrow{\mathrm{E}} \times \overrightarrow{\mathrm{B}}\)

Answer:

(d) Parallel to \(\overrightarrow{\mathrm{E}} \times \overrightarrow{\mathrm{B}}\)

Question 29.

The torque (\(\vec{\tau}\)) experienced by a current-loop of magnetic moment (\(\overrightarrow{\mathrm{M}}\)) placed in magnetic field \(\overrightarrow{\mathrm{B}}\) is

(a) \(\vec{\tau}=\overrightarrow{\mathrm{M}} \times \overrightarrow{\mathrm{B}}\)

(b) \(\vec{\tau}=\overrightarrow{\mathrm{B}} \times \overrightarrow{\mathrm{M}}\)

(c) \(\vec{\tau}=\frac{\vec{M}}{\vec{B}}\)

(d) \(\vec{\tau}=\overrightarrow{\mathrm{M}} \cdot \overrightarrow{\mathrm{B}}\)

Answer:

(a) \(\vec{\tau}=\overrightarrow{\mathrm{M}} \times \overrightarrow{\mathrm{B}}\)

Question 30.

The height of the TV tower at a certain place is 245 m. The maximum distance up to which its programme can be received is

(a) 245 m

(b) 245 km

(c) 56 km

(d) 112 km

Answer:

(c) 56 km

Question 31.

The value of the angle of dip at the earth’s magnetic pole is

(a) 0°

(b) 45°

(c) 90°

(d) 180°

Answer:

(c) 90°

Question 32.

The Boolean expression for NAND gate is

(a) Y = A + B

(b) Y = A . B

(c) Y = \(\overline{A+B}\)

(d) Y = \(\overline{\mathrm{A.B}}\)

Answer:

(d) Y = \(\overline{\mathrm{A.B}}\)

Question 33.

If +q charge is placed inside any spherical surface then total flux coming out from whole surface will be

(a) q × ε_{0}

(b) \(\frac{q}{\varepsilon_{o}}\)

(c) \(\frac{\varepsilon_{o}}{q}\)

(d) \(\frac{q^{2}}{\varepsilon_{o}}\)

Answer:

(c) \(\frac{\varepsilon_{o}}{q}\)

Question 34.

In an alternating current circuit, the phase difference between current I and voltage is Φ, then the Wattless component of current will be

(a) I cos Φ

(b) I tan Φ

(c) I sin Φ

(d) I cos^{2} Φ

Answer:

(c) I sin Φ

Question 35.

Equivalent focal length of two lenses in contact having power -15D and +5D will be

(a) -20 cm

(b) -10 cm

(c) +10 cm

(d) +20 cm

Answer:

(b) -10 cm