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# ICSE Class 8 Answered

<div>1)why does an electric fuse need to melt when large amount of current is passed?</div> <div>2)The electrical appliance is marked with its power and potential difference.please explain</div> <div>3)what is fuse rating?</div>
Asked by Protyusha | 04 Sep, 2016, 10:06: AM
Expert Answer
1)Why does an electric fuse need to melt when large amount of current is passed?
• An electric fuse is a safety device which protects the appliances connected through it from destructive effects of overloading.
• Overloading is the phenomenon which occurs when the main supply of electric current supplies excessive voltage to the circuit.
• When large amount of voltage and current is passing through the circuit, heat energy is evolved due to the corresponding high resistance to the flow.
• This evolution of heat energy is governed by Joule's law of heating as  where 'H' is the heat energy, 'I' is the amount of current, 'R' is the resistance and 't' is the time for which the current flows through the circuit.
• This heating effect of electric current leads to the melting down of the fuse wire which on melting disconnects the mains supply from the domestic circuit,
• Thereby, preventing the domestic appliances from being destroyed due to excessive supply of current.
3)What is fuse rating?
• A fuse wire permits the flow of current through it only up to a definite limit which is called the current rating of the fuse.

2)Electrical appliance is marked with its power and potential difference.
• All the electrical appliances available in the market are marked with the required power and the range of potenital difference or voltage supply which is needed by the appliances to function.
• This marking is very essential in terms of determining the compatibility of the appliance with the electric circuit.
• Potential difference or voltage is the work done by the circuit to move a unit charge once through the circuit and hence allow the electric current to flow.Its SI unit is Volt
• Electric power is the rate at which electric current is supplied by the circuit to the respective appliances.Its unit is Watt

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