# Bihar Board Physics Exam Answer Key 2019 Set-f

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**The resistance of an ideal ammeter is- Zero****Light owes its color to its- Frequency****The Boolean expression for NAND gate is- Y = A.B****The wavefront due to the point source at a finite distance from the source is- Spherical****The height of a TV tower at a certain places to 245m the maximum distance up to which its program can be received is- 56Km****In an alternating current circuit the phase difference between current and voltage is V then the wattless component of current will be –1 SINϕ Option C****Equivalent focal length of two lens in contact having power- 15 D and + 5D will be – (-)10****Deviation of a thin prism of refractive index n and angle of prism A is- -(n-1)A****A Convex lens made from such material which refractive index is 1.5. This lens is immersed in water (u=1.33), then behaves like as- Converging Lens****Unit of surface charge density is –***Cm*^{–2}**With the increase of temperature resistivity of semiconductor –Decreases****The Solar spectrum is- Continuous****The magnifying power of an astronomical telescope for normal adjustment is – Option A****When two bulbs of power 60w and 40w are connected in series then power of the combination will be – 24W****Electric potential in an equatorial position of an electric dipole is- Zero****If Q is equal to charge is placed inside in a spherical surface then total flux coming out from the whole surface will be-****q****/****E**_{0}**The torque experienced by a current loop of magnetic moment M placed in a magnetic field is – M*B Option A****At constant potential difference resistance of an electric circuit is half the value of heat produced will be Double / Two times****The energy of a photon of wavelength λ is – hc/λ****The time in which radioactive substance become half of its initial amount is called – Half-Life****The Stored energy of capacitor changed to 100 volt is 1-joule capacitance of the capacitor is-2×10**^{-4}F**Cylindrical lenses are used to correct eye defect called- Astigmatism****In Earth’s magnetic field Bh a frequency of oscillation of magnetic needle is in then –**N^{2}α B_{h (B)}**Two point charges of class 10 and minus 10 are placed at a distance 40 cm and potential energy of a system will be -25J****The susceptibility of a paramagnetic substance is – Constant****The direction of propagation of the electromagnetic wave is – Option D****The value of an angle of dip at Earth’s magnetic pole is- 90 Degree****The current flowing in the wire is one ampere is a charge of an electron is 1.6×10^19 coulombs the number of electrons flowing through wire per second is –****6.25*10^18****Which one of the following has a maximum refractive index – Diamond****The ratio of root mean square value and peak value of alternating current is –***1√2(*Option B)**The modulation index in an Amplitude Modulation- Lies between zero and 1****Working of the dynamo is based on the principle of-****Electromagnetic Induction****Power of an electric circuit is – V**^{2}/R**The power of an l-r circuit is – B****In a step up Transformer number of turns in primary and secondary cells and N1 and N2 then- N2>N1**