Explore comprehensive UPSC Prelims topic-wise questions on Physics, specifically focusing on Electricity and Magnetism. This resource offers a curated collection of questions, designed to enhance your understanding and preparation for the UPSC Preliminary Examination. Delve into key concepts such as electric fields, circuits, magnetic fields, electromagnetic induction, and more. Each question is strategically crafted to test your knowledge and analytical skills, aligning with the UPSC exam pattern. By engaging with these questions, aspirants can strengthen their grasp on fundamental principles and boost their confidence for the exam. Whether you’re a beginner or an experienced candidate, this resource serves as an invaluable tool to assess your readiness and fine-tune your preparation strategy for the Physics segment of the UPSC Prelims.
Q1. Domestic electrical wiring is basically a (1996)
(a) series connection
(b) parallel connection
(c) combination of series and parallel connections
(d) series connection within each room and parallel connection elsewhere
Ans. (b)
Domestic electrical wiring primarily utilizes a parallel connection setup. This configuration ensures that if one appliance malfunctions, others can continue operating normally. In a parallel connection, each appliance maintains the same potential difference across it, while the currents through different appliances may vary. Consequently, each appliance can draw the required current independently. Therefore, if one appliance fails, the rest of the circuit remains unaffected.
Q2. Assertion (A) Transformer is useful for stepping up or stepping down voltages. Reason (R) Transformer is a device used in DC circuits. (1996)
Codes
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not a correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Ans. (c)
The assertion (A) that transformers are useful for adjusting voltage levels is true, while the reason (R) that transformers are used in DC circuits is false. Transformers are indeed employed to step up or step down voltages in AC circuits. They consist of primary and secondary coils, and the voltage alteration depends on the relative number of turns in these coils. However, transformers cannot function in DC circuits because DC does not induce changes in magnetic field lines necessary for transformer operation.
Q3. Which one of the following is paramagnetic in nature? (1997)
(a) Iron
(b) Hydrogen
(c) Oxygen
(d) Nitrogen
Ans. (c)
Oxygen exhibits paramagnetic behavior. When subjected to a magnetic field, oxygen displays weak magnetism aligned with the field direction. This paramagnetism arises from the spinning motion of its electrons. Paramagnetic substances are those weakly attracted to a magnet. In contrast, substances strongly attracted to a magnet, like iron, are termed ferromagnetic. Hydrogen and nitrogen, on the other hand, exhibit diamagnetic properties as they are weakly repelled by magnetic fields.
Q4. A fuse is used in main electric supply as a safety device. Which one of the following statements about the fuse is correct? (1998)
(a) It is connected in parallel with the main switch
(b) It is made mainly from silver alloys
(c) It must have a low melting point
(d) It must have a very high resistance
Ans. (c)
The correct statement regarding a fuse is option (c). A fuse serves as a safety device in electrical circuits, particularly in domestic setups, to prevent short circuits and overloads. Typically made of a metal with a low melting point, the fuse wire melts when the current exceeds a safe limit, thereby breaking the circuit. This action safeguards against potential hazards such as fires due to overheating caused by short circuits or excessive current draw.
Q5. Assertion (A) The temperature of a metal wire rises when an electric current is passed, through it. Reason (R) Collision of metal atoms with each other releases heat energy. (1998)
Codes
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Ans. (c)
Assertion (A) is true, while reason (R) is false. When an electric current passes through a metal wire, the wire’s temperature increases. This temperature rise occurs due to the kinetic energy transferred from the accelerated electrons to the metal atoms through collisions. The collisions between electrons and metal ions or atoms lead to an increase in the average kinetic energy of the atoms, resulting in a temperature rise. However, the reason provided, stating that the collision of metal atoms releases heat energy, is incorrect.
Q6. Consider the following statement. (1999)
An ordinary light bulb has a rather short life because the
1. Filament wire is not uniform.
2. Bulb cannot be evacuated completely.
3. Wires supporting the filament melt at high temperature.
Which of the above statements are correct?
(a) 1 and 3
(b) 2 and 3
(c) 1 and 2
(d) All of these
Ans. (d)
All the statements (1, 2, and 3) are correct regarding the short lifespan of an ordinary light bulb. The filament wire’s lack of uniformity can lead to uneven heating, causing certain parts to overheat and fail prematurely. Additionally, the inability to completely evacuate the bulb leads to the presence of gases that can react with the filament, accelerating its degradation. Finally, the supporting wires of the filament may melt at high temperatures, contributing to the bulb’s shorter lifespan.
Q7. Fluorescent tubes are fitted with a choke. The choke coil (2000)
(a) steps up the line voltage
(b) steps-down the line voltage
(c) reduces current in the circuit
(d) chokes low frequency current
Ans. (c)
The correct option is (c). Fluorescent tubes are equipped with a choke coil, which functions to reduce the current in the circuit. This coil, typically made of thick insulated copper wire wound around a soft iron core, offers significant inductance and reactance, thereby effectively limiting the alternating current in the circuit. However, the choke coil does not influence voltage regulation; instead, it primarily affects current flow.
Q8. Two wires have their lengths, diameters and resistivities all in the ratio of 1:2. If the resistance of the thinner wire is 10 Ω, then the resistance of the thicker wire is (2001)
(a) 5 Ω
(b) 10 Ω
(c) 20 Ω
(d) 40 Ω
Ans. (b)
The resistance of the thicker wire is 10 Ω, as stated in option (b). When two wires have lengths, diameters, and resistivities in a ratio of 1:2, the resistance is solely determined by the wire’s geometry and resistivity. Since the thicker wire has twice the diameter and length of the thinner wire, its resistance will be the same as the thinner wire, which is given as 10 Ω.
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