Give reasons for the following :
(i) There is either a convergence or a divergence of magnetic field lines near the ends of a current carrying straight solenoid.
(ii) The current carrying solenoid when suspended freely rests along a particular direction.
(iii) The burnt out fuse should be replaced by another fuse of identical rating.
Give reasons for the following :
(i) There is either a convergence or a divergence of magnetic field lines near the ends of a current carrying straight solenoid.
(ii) The current carrying solenoid when suspended freely rests along a particular direction.
(iii) The burnt out fuse should be replaced by another fuse of identical rating.
(i) Inside a current-carrying solenoid, the magnetic field lines are in the form of parallel straight lines, indicating that the magnetic field is uniform (the same at all points). Near the ends of the solenoid, these field lines either diverge (at the north-seeking pole) or converge (at the south-seeking pole) because the solenoid behaves like a bar magnet, where the field lines must emerge from the north pole, spread out into the surrounding space, and merge at the south pole to form closed curves.
(ii) A current-carrying solenoid behaves exactly like a bar magnet, where one end acts as a magnetic north pole and the other end acts as a magnetic south pole. When suspended freely, it aligns itself along the Earth's geographic North-South direction due to the directive property of magnets.
(iii) A fuse is a safety device based on the heating effect of electric current. It must be replaced by another fuse of identical rating because:
- If a fuse of a higher rating is used, it will not melt and break the circuit when an excessive, unsafe current flows, which can damage appliances or cause an electrical fire.
- If a fuse of a lower rating is used, it will melt and break the circuit even during normal, safe operating currents, causing frequent and unnecessary power interruptions.
Marking Scheme
- 11 Mark: Correct explanation of convergence/divergence near the ends of the solenoid (mentioning uniform field inside and bar-magnet-like behavior outside).
- 21 Mark: Correct explanation of the directive property of the suspended solenoid (mentioning it behaves like a bar magnet with North and South poles aligning with Earth's magnetic field).
- 31 Mark: Correct explanation of why an identical fuse rating is necessary (explaining the risks of using higher or lower rating fuses).
Hint
Recall how the magnetic field lines of a solenoid compare to those of a bar magnet, and think about the safety hazards of using an incorrect fuse rating.
Quick Oral Answer
A current-carrying solenoid behaves exactly like a bar magnet, having a uniform magnetic field inside represented by parallel straight lines. When suspended freely, it aligns in the North-South direction. A fuse must be replaced with an identical rating to ensure it melts precisely when the current exceeds the safe threshold, protecting the circuit from overloading.
Analysis & Explanation
This question evaluates the student's understanding of the magnetic field pattern of a solenoid and the practical safety applications of electric fuses.
- Solenoid Field Pattern: According to the NCERT text, the magnetic field lines inside a solenoid are parallel straight lines, indicating a uniform field. Outside, the pattern is identical to that of a bar magnet. Thus, at the ends, the transition from a uniform internal field to a divergent/convergent external field occurs as the lines form closed loops.
- Directive Property: Since the solenoid behaves like a bar magnet with distinct north-seeking and south-seeking poles, it experiences a restoring torque in the Earth's magnetic field, aligning it along the North-South direction.
- Fuse Rating: A fuse wire has a specific melting point and resistance designed to melt when the current exceeds its rated value (). Altering this rating defeats its purpose as a safety interlock.
Common Mistakes
- 1Failing to mention that the magnetic field inside the solenoid is uniform (parallel straight lines).
- 2Vaguely stating that the solenoid aligns 'in a direction' without specifying the North-South direction.
- 3Believing that a higher rating fuse is 'safer' or 'better' because it won't blow easily, ignoring the fire hazard it creates.
Interesting Facts
The unit of magnetic field strength is named the 'oersted' in honor of Hans Christian Oersted, who accidentally discovered electromagnetism in 1820 when a compass needle deflected near a current-carrying wire.
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Frequently Asked Questions
How many marks does this question carry in CBSE Class 10 Science 2020?
This question carries 3 marks in the CBSE Class 10 Science 2020 examination.
Which chapter does this question come from in Science?
This question is from the chapter "Magnetic Effects of Electric Current" in the CBSE Class 10 Science syllabus.
What topic does this question cover in Science?
This question covers the topic "Magnetic Field due to a Current in a Solenoid and Fuse Safety" from CBSE Class 10 Science.
What type of question is this in the CBSE Class 10 Science 2020 paper?
This is a Short Answer question from Section B in the CBSE Class 10 Science 2020 paper.