Question

What is the current through an electric appliance of rating 5KW, 200V, and can you use a fuse which is rated 8A?
A) 25 A, yes
B) 2.5A, yes
C) 25A,no
D) 2.5A, no

Answer 1

Hint: The current in the circuit is given as current \[I = \dfrac{{power}}{{voltage}}\], fuses which have designed so that our appliances could be prevent from burning or short-circuiting. A fuse which is rated as 8 A can be applied where the current flowing is less than 8 A, if it is applied where the current is flowing \[I = 25A\], the fuse will blow off very prior to application of appliance hence it will not serve our requirement.

Complete step by step answer:
To prevent these electrical overloads, fuses are delicately designed to trip or blow, stopping the flow of current to the overloaded wire.
The fuse must always be connected to the mains and it must be of the correct value.
For instance, a fuse that is designed to carry a maximum load of 8Aof current will be blown if the current in the circuit particularly where we have placed the fuse exceeds 8A. due to which the circuit is incomplete hence we would protect our appliances.
Here, the current through the appliances is given by, current \[I = \dfrac{{power}}{{voltage}}\]
\[ \Rightarrow I = \dfrac{P}{V}\] …………..…………. eq .(1)
\[ \Rightarrow P = 5kW = 5000W\]
\[ \Rightarrow V = 200V\]
Putting all the values in eq.(1)
\[ \Rightarrow I = \dfrac{P}{V} = \dfrac{{5000}}{{200}}A\]
\[ \Rightarrow I = 25A\]
Since the current in the circuit is \[I = 25A\], the fuse of 8 A can not be used because the current through the appliance is greater than the fuse rating.

When the current of \[I = 25A\], is flown through the circuit the fuse will blow off and it will not be able to fulfill our requirement. Hence option (C) is the correct answer.

Note:
Since fuses are the safety devices that are built to protect our electrical appliances from overloading and subsequent damages.
If there were no fuses and we operated too many appliances on a single circuit, the wire carrying the power or current for that circuit would get extremely hot, short circuits, and possibly get caught on fire.