(a) Why does an electric bulb become dim when an electric heater in parallel circuit is switched ON?
(b) How to connect three resistors each of resistance 8 Ω, so that the equivalent resistance of the combination is 12 Ω? Draw diagram of the combination and justify your answer.
(a) Why does an electric bulb become dim when an electric heater in parallel circuit is switched ON?
(b) How to connect three resistors each of resistance 8 Ω, so that the equivalent resistance of the combination is 12 Ω? Draw diagram of the combination and justify your answer.
Official answer
(a) When an electric heater in a parallel circuit is switched ON, the resistance of the circuit decreases, causing the current to increase. As a result, the voltage across the electric bulb decreases, causing it to become dim.
(b) To connect three resistors each of resistance 8 Ω, so that the equivalent resistance of the combination is 12 Ω, we can connect two resistors in parallel and the third resistor in series with the parallel combination.
Marking scheme
- 1.None
Hint
(a) Think about how the resistance of the circuit affects the current and voltage. (b) Consider the different combinations of resistors and how they affect the equivalent resistance.
Quick oral answer
The electric bulb becomes dim because the voltage across it decreases when the electric heater is switched ON. To connect three resistors each of resistance 8 Ω, so that the equivalent resistance of the combination is 12 Ω, we can connect two resistors in parallel and the third resistor in series with the parallel combination.
Common mistakes
- 1.thinking that the electric bulb becomes dim because the current increases
- 2.not considering the effect of the electric heater on the resistance of the circuit
Analysis and explanation
(a) The electric bulb becomes dim because the voltage across it decreases when the electric heater is switched ON.
(b) The combination of resistors is justified because the equivalent resistance of the parallel combination of two 8 Ω resistors is 4 Ω, and when the third 8 Ω resistor is connected in series, the total equivalent resistance becomes 12 Ω.
Interesting facts
The concept of parallel circuits is used in many real-life applications, such as household wiring.
The equivalent resistance of a parallel combination of resistors is always less than the resistance of any individual resistor.
Question details
Q37 of 39 questions
- Board
- CBSE
- Class
- Class 10
- Subject
- Science
- Year
- 2026
- Section
- Section C
- Marks
- 3
- Type
- Short Answer
- Chapter
- Electricity
- Topic
- Electric Circuits
- Bloom's level
- Analyzing
- Syllabus topic
- Electricity
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Frequently asked questions
How many marks does this question carry in CBSE Class 10 Science 2026?
This question carries 3 marks in the CBSE Class 10 Science 2026 examination.
Which chapter does this question come from in Science?
This question is from the chapter "Electricity" in the CBSE Class 10 Science syllabus.
What topic does this question cover in Science?
This question covers the topic "Electric Circuits" from CBSE Class 10 Science.
What type of question is this in the CBSE Class 10 Science 2026 paper?
This is a Short Answer question from Section C in the CBSE Class 10 Science 2026 paper.