Class 10 Science, Chapter 11 (NCERT). 15 questions by concept. Open “Show answer” for the answer and why.
How to teach this chapter · Common misconceptions & worked visual for this chapter
In a metal wire carrying current, how does the direction of conventional current compare with the direction of electron drift?
(b) Opposite
Conventional current is taken to flow from positive to negative outside the cell, but electrons, being negatively charged, drift from negative to positive. So conventional current and electron drift are in opposite directions.
A battery symbol in a circuit diagram has three long-and-short line pairs side by side. How many cells does it stand for?
(d) Three
Each long-and-short line pair is the symbol for one cell. Three pairs side by side stand for three cells joined together, which make a battery.
A charge of 600 C passes through a conductor in 5 minutes. What is the current?
(b) 2 A
Current is charge divided by time: I=Q/t. First convert 5 minutes to 300 s. Then I = 600/300 = 2 A.
How is an ammeter connected in a circuit, and what should its resistance be?
(c) In series, very low resistance
An ammeter is always connected in series, so the current to be measured passes through it. It is given a very low resistance so it does not change the current in the circuit.
An 8 V battery moves 2 C of charge through a circuit. How much energy does it supply?
(c) 16 J
Use W = V × Q. The energy supplied is 8 V × 2 C = 16 J.
One volt equals one what?
(a) Joule per coulomb
One volt is one joule per coulomb, the energy given to each unit of charge. Coulomb per second is the ampere, the unit of current, not voltage.
A current of 0.5 A flows through a resistor of 8 ohms. What is the potential difference across it?
(a) 4 V
Use V = IR. Here I = 0.5 A and R = 8 ohms, so V = 0.5 x 8 = 4 V.
A V–I graph is a straight line through the origin with slope 5 V/A. What is the resistance?
(d) 5 Ω
With V on the vertical axis, the slope V/I is the resistance: 5 Ω. Its reciprocal, 0.2, would be the conductance.
A wire has a resistance of 18 Ω. A second wire of the same material and length, at the same temperature, has three times the cross-sectional area. What is its resistance?
(d) 6 Ω
Using R = ρL/A with the same material, length and temperature, resistance is inversely proportional to area. Three times the area gives one-third the resistance: 18 Ω ÷ 3 = 6 Ω.
A copper wire is replaced by a longer copper wire of the same thickness. What happens to the resistance?
(d) It increases
Resistance is proportional to length, so the longer wire has more resistance. Its resistivity, a property of copper, is unchanged.
Resistors of 2 Ω and 6 Ω are connected in series across a battery. How do the voltages across them compare?
(b) The 6 Ω resistor has three times the voltage of the 2 Ω resistor
In series the same current flows through both resistors, so each voltage drop is V = IR. The 6 Ω resistor has three times the resistance, so it has three times the voltage.
Two resistors of unequal resistance are connected in parallel across the same battery. How do their currents compare?
(c) The branch with lower resistance carries more current
In a parallel connection, both resistors have the same potential difference across them. Since current equals potential difference divided by resistance, the branch with lower resistance carries more current.
How is a fuse connected in a circuit, and what makes it melt?
(d) In series; melts when heating from the current becomes too high.
A fuse is connected in series so the full line current passes through it. When the current becomes too high, heating in the fuse wire rises sharply and it melts, breaking the circuit.
At fixed resistance and fixed time, the current through a resistor doubles. By what factor does the heat produced change?
(a) 4 times
Heat produced is given by H=I²Rt. With R and t fixed, H depends on I squared. Doubling I makes I² four times larger, so heat becomes 4 times larger.
A current of 2 A flows through a 5 Ω resistor. What power is used?
(b) 20 W
P = I²R = 2² × 5 = 20 W. Using IR² instead gives 50 W, which is wrong.
Wrong
Less current flows just after a 4 Ω resistor than just after a 2 Ω resistor in the same series loop.
Why it feels right. I treat current like something the components use up.
Right
In a steady series loop, the same charge per second passes each point. The potential drops can differ.
Worked example
