Polytechnic Physics Set 12

221. The SI unit of potential difference is

Ampere Volt Coulomb Joule

Answer: Volt

222. 1 Ohm is equal to

1 Volt / 1 Ampere 1 Volt x 1 Ampere 1 Volt / 1 Ampere 1 Volt x (1 Ampere)²

Answer: 1 Volt / 1 Ampere

223. If the length of a metal wire is doubled, then the resistance of the wire

Becomes half Becomes double Becomes less than one-fourth Becomes four times

Answer: Becomes double

224. The SI unit of resistivity is

Ωm⁻¹ Ω⁻¹m⁻¹ Ω Ωm

Answer: Ωm

225. When resistors are connected in series, then

The current in each resistor is the same as the circuit current The voltage across each resistor is the same as the total circuit voltage The sum of currents in each resistor equals the total circuit current The effective resistance is less than the smallest individual resistance

Answer: The current in each resistor is the same as the circuit current

226. When two resistors R₁ and R₂ are connected in parallel, the equivalent resistance (Rp) of the parallel combination is

Rp = (R₁ + R₂) / R₁R₂ Rp = R₁R₂ / (R₁ – R₂) Rp = (R₁ – R₂) / (R₁ + R₂) Rp = R₁R₂ / (R₁ + R₂)

Answer: Rp = R₁R₂ / (R₁ + R₂)

227. According to Joule’s law of heating, the heat generated by electric current is given by

H = I²RT H = IRT H = IR²t H = IR²

Answer: H = I²RT

228. 1 Watt of electric power is equal to

1W = 1V x 1A 1W = 1A / 1V 1W = 1V / 1A 1W = 1V² / 1A

Answer: 1W = 1V x 1A

229. The commercial unit of electric energy is

kilowatt/hour kilowatt-hour kilowatt/hour² kilowatt/(hour)²

Answer: kilowatt-hour

230. The resistivity of a wire

is directly proportional to its cross-sectional area is inversely proportional to its cross-sectional area is independent of its cross-sectional area is proportional to the square of its cross-sectional area

Answer: is inversely proportional to its cross-sectional area

231. Electrical heating appliances such as bread toasters and electric irons are made using alloys instead of pure metals because

alloys have lower resistivity alloys have higher resistivity it does not depend on resistivity None of the above

Answer: alloys have higher resistivity

232. A current flows through a horizontal power wire from east to west. The direction of the magnetic field at a point directly below the wire is

north to south south to north west to east east to west

Answer: north to south

233. The magnetic field due to a circular coil carrying electric current with n turns is

n² times the amount produced by a single turn n times the amount produced by a single turn 1 time the amount produced by a single turn equal to the amount produced by a single turn

Answer: n times the amount produced by a single turn

234. The strong magnetic field produced inside a solenoid can be used to magnetize a magnetic material like a piece of soft iron placed inside the coil. The magnet thus formed is called

permanent magnet temporary magnet electromagnet natural magnet

Answer: temporary magnet

235. The magnetic field inside a long straight solenoid carrying electric current

is zero decreases as we move towards the end increases as we move towards the end is the same at all points

Answer: is the same at all points

236. According to Fleming’s left-hand rule, the direction of the forefinger indicates

electric current magnetic field generated force motion of the conductor

Answer: magnetic field

237. The device that can detect the presence of electric current in a circuit

voltmeter galvanometer resistor diode

Answer: galvanometer

238. The basic phenomenon underlying the working of an electric generator is

electromagnetic induction Hall effect ferroelectric effect photoelectric effect

Answer: electromagnetic induction

239. A rectangular coil of copper wire is rotated in a magnetic field. The direction of the induced electric current changes every _____.

2 rotations 1 rotation ½ rotation ¼ rotation

Answer: 2 rotations

240. Magnetic field lines are shown together where the magnetic field is _____.

strong weak uniform D) none of the above

Answer: strong