(a) State Fleming's Left-hand rule.

(b) List three characteristic features of the electric current used in our homes.

(c) What is a fuse? Why is it called a safety device?

(d) Why is it necessary to earth metallic electric appliances?

Magnetic Effects of Electric Current

Fleming's Left-hand Rule and Domestic Electric Circuits

Official Answer

(a) Fleming's Left-hand Rule:

According to this rule, stretch the thumb, forefinger, and middle finger of your left hand such that they are mutually perpendicular to each other. If the first finger (forefinger) points in the direction of the magnetic field and the second finger (middle finger) points in the direction of the current, then the thumb will point in the direction of motion or the force acting on the conductor.

(b) Three characteristic features of the electric current used in our homes (in India):

Alternating Current (AC): The current supplied to our homes is alternating in nature, meaning it reverses its direction periodically.
Frequency: The frequency of this alternating current is $50\text{ Hz}$ , which means it changes its direction every $1/100\text{ s}$ (or $100$ times in one second).
Voltage: The potential difference (voltage) between the live wire and the neutral wire is maintained at $220\text{ V}$ .

(c) Fuse and its role as a safety device:

What is a fuse? A fuse is a safety device consisting of a short wire made of a metal or an alloy of an appropriate low melting point (such as lead-tin alloy) connected in series with the live wire.
Why is it called a safety device? When an excessively high current flows through the circuit due to overloading or short-circuiting, the fuse wire heats up, melts, and breaks the circuit. This prevents damage to the electrical appliances and avoids potential electrical fires.

(d) Necessity of earthing metallic electric appliances:

Metallic appliances (like electric irons, refrigerators, and toasters) are earthed by connecting their metallic bodies to the earth wire (which is buried deep in the earth). This provides a low-resistance conducting path for any leakage current. If the insulation of a live wire gets damaged and touches the metallic body of the appliance, the current flows safely to the earth rather than passing through the body of a user touching the appliance, thereby preventing a severe electric shock.

mutually perpendicularforefingermiddle fingerthumbalternating current220 V50 Hzlow melting pointbreaks the circuitlow-resistance pathleakage currentelectric shock

Marking Scheme

1State Fleming's Left-hand rule correctly: 1.5 Marks
2List three features of domestic current: 1.5 Marks (0.5 Mark for each feature)
3Define fuse and explain why it is a safety device: 1 Mark
4Explain the necessity of earthing metallic appliances: 1 Mark

Hint

For (a), think of the three mutually perpendicular fingers of your left hand. For (b), recall the voltage and frequency of domestic AC in India. For (c) and (d), focus on how melting points and low-resistance paths prevent hazards.

Quick Oral Answer

Fleming's Left-hand rule is used to find the direction of force on a current-carrying conductor in a magnetic field. Earthing is necessary because it safely diverts any leakage current from a metallic appliance to the ground, protecting us from electric shocks.

Analysis & Explanation

This question tests the fundamental understanding of electromagnetic force rules and domestic electrical safety.

Part (a) directly uses the definition of Fleming's Left-hand rule from the NCERT text, which relates the mutually perpendicular directions of magnetic field, current, and force.
Part (b) outlines the standard parameters of domestic AC supply in India ( $220\text{ V}$ , $50\text{ Hz}$ ).
Part (c) and (d) focus on safety mechanisms. A fuse acts as a weak link that breaks under high thermal stress (Joule heating) to protect expensive appliances. Earthing ensures that the metallic casing of an appliance remains at zero potential (earth potential), eliminating the risk of shock from leakage currents.

Common Mistakes

1Confusing the left-hand rule with the right-hand rule.
2Writing that the frequency of AC in India is $60\text{ Hz}$ instead of $50\text{ Hz}$ .
3Believing that earthing reduces electricity bills rather than acting as a safety mechanism to prevent shocks.

Interesting Facts

The earth wire is traditionally color-coded green (or green with a yellow stripe) to distinguish it from the live (red/brown) and neutral (black/blue) wires.

A fuse wire must always be connected in series with the live wire, never the neutral wire, to ensure the appliance is completely isolated from the high voltage when the fuse blows.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2020?

This question carries 5 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 "Fleming's Left-hand Rule and Domestic Electric Circuits" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2020 paper?

This is a Long Answer question from Section C in the CBSE Class 10 Science 2020 paper.