12th Physics Answer Key 2021|Bihar Board Objective Answer All Set 2021
1.The relative Permittivity (E r) of a medium is
(A) E / E 0 (B) E x E0 (C) E+E 0 (D) E-E0
2.The Value of Electric Potential at a distance r from a point charge q is
(A) 1/ 4 he0 + q/r (B)1/4 h E0 .q/r2 (C) q.r / 4h E0 (D) 1/4HE0.q2 /r
6. One ampere is equal to
A) 1 Coloumb / 1Second B) 1 Coloumb X 1 Second C) 1 Volt X 1 Ohm D) 1 Ohm / 1 Volt
7. Unit of Electromotive force is
A)Newton B) Joule C) Volt D) newton / ampere
8. The heat produced in a conductor of resistance R due to flow of current I for time t is
A) I . R .t b) I . R2 .t C) I2 . R. t d) I2 . R2 . t
9. Magnetic field of 5 tesla is equal to
A) 5 x weber / ( meter) 2 B) 5x 105 weber / ( meter) 2 C) 5×102 weber / ( meter) 2 D) 5×102 weber x ( meter) 2
10. The relation between r.m.s value of alternating current ( I r.m.s) and peak value of alternating current (Io) is
A) I r.m.s = 0.505 I0 b) I r.m.s = 0.606 I0 c) I r.m.s = 0.707 I0 d) I r.m.s = 0.808 I0
12. Which of the following relations is correct for power factor ?
A) Power factor = True Average Power X Apparent Average Power B) Power Factor = Apparent Average Power / True Average power C ) Power Factor = True Average Power / Apparent average power d) Power Factor = 1/2 [ True average powerXApparent average power ]
13.Value of the green color code on carbon resistance is
A) 3 B) 4 C) 5 D) 6
14. Expression of force on a charge q move with velocity V> in a magnetic field B> is
A) B) C) D)
15. Which of the following is correct for transformer ?
A) It converts A.C into D.C B) It Converts D.C into A.C C) It increase of Decrease D.C Voltage D) It increase or decrease A.C Voltage
16. S.I Unit of magnetic pole strength is
A) N B) N/A.M C) A.m D) A.m / N
17. The value of angle of dip at magnetic pole of the earth is
A) 0o B) 90o C)45o D)180o
18.The value of magnetic susptibility of vacuum is
A) equal to 0.5 B) infinite C) equal to one d) zero
19.Which of the following relations is correct for permeability?
A) y = H/B b) y = B/H c) y = B.H d) y = (B+H)
20.If B is earth’s magnetic field in magnetic meridian, o is angle of dip, B H is horizontal component of B > and BV is vertical component of B>, then which of the following relations is correct?
A) BH = BCOSo B) BV = BCOSo c)BH+BSing0 D) BV =BH SIN0
21. The direction of propagation of electromagnetic wave is
A) parallel to E> B) parallel to B> C) parallel to (B> x E> ) D) parallel to (E> x B>)
22. The unit of which physical quantity is light year?
A) Distance B) Time C) Energy D) Intensity of Light
23. The image formed by simple microscope is
A) Virtual and erect B) Virtual and inverted C) Real and erect D) Real and inverted
24.Which of the following eye defects is removed by convex lens?
A) Nearsightendness B)Farsightedness C)Presbyopia D) Astimatism
28.Focal lengthof eye-lens of a healthy man is about
A) 1mm B) 2cm C) 25cm D)1m
29. Interference of light is the redistribution of which of the following physical quantities ?
A) Frequency B) Intensity C) Wavelength D) Speed
30. The rest mass of photon is
A) Zero B)infinite C) 9-1 x 10 -31 kg D) 1.6 X 10-27 kg
31. Bohr’s frequency condition is
A) E1 – E2 = 1/2 hv B)E1 – E2 = hv C)E1 – E2 = 3hv D) E1 – E2 = 3/2 hv
35. The decimal number of binary number (1001)2 is
A) (12) 10 B) (18) 10 C) (9) 10 D) (25) 10
36. Which of the following represents the a- decay of A X?
A) B) c) D)
37.Which of the following is not a fundamental particle?
A) Neutron B) Proton C)a-particle D) Electron
38. Which of the following is the frequency range for TV broadcasting?
A) 30-300 Hz B) 30-300k HZ C) 30-300 MHz D) 30-300GHz
39.Which of the following units is correct to measure attenuation?
A) Decibel B) Ohm C) Ampere D) Volt
40.A p – type semiconductor is
A) positively charge B) negatively charge C) uncharged D) uncharged at absolute zero temperature but charged at the high temperature
41. The minimum orbital angular momentum of an electron in hydrogen atom is
