Question 3 - Case Based Questions (MCQ) - Chapter 12 Class 10 - Electricity

In the given circuit, connect a nichrome wire of length ‘L’ between points X and Y and note the ammeter reading Answer any four questions from (a) to (e).

Question 3 (a)

When this experiment is repeated by inserting another nichrome wire of the same thickness but twice the length (2L), what changes are observed in the ammeter reading? 

(i) Ammeter reading will increase

(ii) Ammeter reading will decrease

(iii) Will show double the increase

(iv) No change in ammeter reading

Answer:

Resistance is directly proportional to length of the conductor.

So, if length is increased , resistance increases .

If resistance increases, current decreases .

Therefore, the ammeter reading will decrease.

So, the correct answer is (ii).

Question 3 (b)

State the changes that are observed in the ammeter reading if we double the area of crosssection without changing the length in the above experiment. 

(i) Ammeter reading will increase

(ii) Ammeter reading will decrease

(iii) Will decrease half

(iv) No change in ammeter reading

Answer:

Resistance of a conductor is inversely proportional to area of cross section.

So, if the area of the cross section increases , resistance decreases.

If resistance decreases, current increases .

Therefore, the ammeter reading will increase.

So, the correct answer is (i).

Question 3 (c)

In a circuit two resistors of 5 Ω and 10 Ω are connected in series. Compare the current passing through the two resistors. 

(i) 1: 2

(ii) 1: 3

(iii) 2: 1

(iv) 1:1

Answer:

In a series connection of resistors, the same current passes through all the resistors.  

Hence, the current will be the same. 

So, Ratio of the currents will be 1: 1 . 

So, the correct answer is (iv).

Question 3 (d)

The instrument used to measure current is ____________. 

(i) Ammeter

(ii) Voltmeter

(iii) Galvanometer

(iv) manometer

Answer:

An instrument that measures electric current in a circuit is an Ammeter.

So, the correct answer is (i).

Question 3 (e)

When nichrome and copper wire of same length and same radius are connected in series and current I is passed through them. Which wire gets heated up more? 

(i) Nichrome wire

(ii) Copper wire

(iii) Both will heat up at the same temperature

(iv) None of the wire will get heated up. 

Answer:

Heat produced, H = I ² R

Where,

• I is the current
• R is the resistance

In a series circuit, the same current passes through both the wires. 

So, Heat produced is directly proportional to the resistance.

For the same length and same radius, the resistance of nichrome wire is more than copper wire due to its higher resistivity. 

Hence, Nichrome wire is heated up more than copper wire.

So, the correct answer is (i).