Question

When electric current flows in a purely resistive circuit electrical energy gets fully converted into heat energy. The amount of heat produced (H) in the circuit is found to be directly proportional to  the square of current (12) the resistance (R) of the conductor and the time (t) for which current flows. In other words H = I2Rt. Electrical devices such an electric fuse, electric heater, electric iron etc. are all based on this effect called heating effect of electric current.

1. List two properties of heating elements.   1
2. List two properties of electric fuse.   1
3. Name the principle on which an electric fuse works. Explain how a fuse wire is capable of saving electrical appliances from getting damaged due to accidently produced high currents.   2
                                      OR
   The power of an electric heater is 1100 W. If the potential difference between the two terminals of the heater is 220 V, find the current flowing in the circuit. What will happen to an electric fuse of rating 5 A connected in this circuit?   2

Answer 1

1. Properties of Heating Elements:
   1. High Resistance: Heating elements are designed to maintain a high level of electrical resistance, which enables the conversion of electrical energy into thermal energy when current passes through them.
   2. Good Heat Resistance: Heating elements should be heat resistant to endure high temperatures during operation.
2. Properties of an Electric Fuse:
   1. Low Melting Point: The fuse wire in an electric fuse can melt at a low temperature. Because of this, the fuse melts quickly when a current that is stronger than its rating value flows through it, cutting the circuit.
   2. Good Conductivity: In a solid state, the fuse wire should maintain adequate electrical conductivity, allowing normal current to pass without significant resistance.
3. Principle of Electric Fuse and How It Works: The electric fuse is heating the electric current. When the current exceeds the rated value, the fuse wire heats up owing to electrical resistance.
   • Fuse Wire's capability to have appliances: 
     1. Low Melting Point: The fuse wire is chosen to have a low melting point.
     2. Quick Melting: When an excess current flows through the circuit, the fuse wire quickly reaches its melting point, causing it to melt and break the circuit.
     3. Interrupts the current: The fuse blocks excessive current flow, preventing damage to electrical appliances.
     4. Protects Devices: The fuse is a sacrificial element that melts to protect electrical appliances and devices in the circuit.
     5. Safety Measure: A fuse is a safety mechanism that prevents fires and protects electronic equipment from damage caused by excessive currents or circuit failures.

OR

c. Power (P) = `(V^2)/R`

R = `(V^2)/P`

R = `48400/1100`

= 44 Ω

Now, current using Ohm's law

I = `V/R = 220/44` = 5 A

Connecting a 5 A electric fuse to this circuit will ensure proper operation. The fuse can tolerate a current of up to 5 A. The circuit's current is exactly 5 A, hence the fuse will not blow and the circuit will continue to function normally. If the current exceeds 5 A, the fuse will blow, protecting the electrical components.