Q90. A 9 V cell is connected to 3 Ω, 2 Ω and 1 Ω resistors in series. What current flows?
[RRB Group D — 6 August 2026, Shift 3]
(A) 9 A
(B) 1.5 A
(C) 3 A
(D) 6 A
Answer: (B) 1.5 A
Explanation: Series resistance is the sum 3 + 2 + 1 = 6 Ω. Applying Ohm’s law to the complete loop gives I = V/R = 9/6 = 1.5 A. Every resistor carries this identical current.
Q89. What is the main function of an electrical fuse in household wiring?
[RRB Group D — 6 August 2026, Shift 2]
(A) Increase source voltage
(B) Interrupt an excessive current
(C) Store electrical energy
(D) Prevent all temperature changes
Answer: (B) Interrupt an excessive current
Explanation: The fuse contains a metal link chosen to melt when current becomes dangerously large. Its melting opens the circuit, helping prevent overheating and fire. It does not stabilize voltage or store charge and must have a suitable current rating.
Q88. On which effect of current does an ordinary fuse primarily operate?
[RRB Group D — 5 February 2026]
(A) Magnetic effect
(B) Chemical effect
(C) Heating effect
(D) Photoelectric effect
Answer: (C) Heating effect
Explanation: A fuse responds to excess current because the resistive element produces heat according to Joule’s law, H = I²Rt. If its temperature reaches the melting point, the connection breaks. The rapid increase of heating with current is vital.
Q87. Which expression gives the dimensional nature of electric charge in terms of current and time?
[RRB NTPC Undergraduate CBT — 9 May 2026]
(A) Current divided by time
(B) Current multiplied by time
(C) Voltage multiplied by resistance
(D) Power divided by time
Answer: (B) Current multiplied by time
Explanation: Electric current is defined as charge passing per unit time, I = Q/t. Rearranging yields Q = It, so the dimensions of charge are those of electric current multiplied by time. Its SI unit is the coulomb.
Q86. In a metallic conductor, the conventional current direction is ____ the direction of electron drift.
[RRB Group D — 29 December 2025]
(A) the same as
(B) opposite to
(C) perpendicular to
(D) unrelated to
Answer: (B) opposite to
Explanation: Electrons have negative charge and drift toward higher electric potential in a simple metal circuit. Conventional current is defined in the direction a positive charge would move, so it is opposite to electron drift. The current convention predates electron discovery.
Q85. What is produced around a wire when electric current passes through it?
[RRB Group D — 14 December 2025]
(A) Only an electric charge
(B) A magnetic field
(C) A vacuum
(D) A permanent temperature decrease
Answer: (B) A magnetic field
Explanation: A current-carrying conductor generates a magnetic field around itself. Its direction can be found with the right-hand thumb rule. The field forms closed curves around a straight wire and provides the basic operating principle of electromagnets.
Q84. What energy conversion occurs in a purely resistive conductor carrying current?
[RRB Group D — 8 December 2025]
(A) Electrical energy into heat
(B) Heat into gravitational energy
(C) Light into electrical energy
(D) Sound into chemical energy
Answer: (A) Electrical energy into heat
Explanation: Moving charge carriers transfer energy to the lattice through collisions, increasing its thermal energy. For a resistance R carrying current I, the heating rate is I²R. This is the intended process in kettles and other resistive heating appliances.
Q83. A 110 W electrical appliance is operated at 220 V. Calculate the current it draws.
[RRB Group D — 5 December 2025]
(A) 0.25 A
(B) 0.5 A
(C) 2 A
(D) 5 A
Answer: (B) 0.5 A
Explanation: Power is the product of potential difference and current, P = VI. Therefore I = 110/220 = 0.5 A. The current is one-half ampere under the stated operating conditions, without requiring the appliance’s resistance to be given.
Q82. Electric current is defined as the rate of flow of which physical quantity?
[RRB Group D — 2 December 2025]
(A) Electrical charge
(B) Electrical resistance
(C) Magnetic flux
(D) Potential difference
Answer: (A) Electrical charge
Explanation: A current of one ampere means one coulomb of charge crosses a section every second. Mathematically, average current equals charge divided by elapsed time. Electrons carry current in metals; ions also transport charge in electrolytes.
Q81. Why is nichrome preferred for electric heating elements?
[SSC CGL — 21 September 2025, Shift 3]
(A) Low resistance and low melting point
(B) High resistivity and high melting point
(C) Perfect conductivity and zero heating
(D) Rapid oxidation and low strength
Answer: (B) High resistivity and high melting point
Explanation: Nichrome has relatively high resistivity, so a useful length generates substantial heat, and its high melting point allows it to tolerate operating temperatures. It also resists oxidation well. These properties distinguish it from an ordinary fuse wire.
