Question:medium
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 (i) the square of current (I2)
(ii) the resistance (R) of the conductor and
(iii) 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.
&
a) List two properties of heating elements.
b) List two properties of electric fuse.
c) 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 accidentally produced high currents.
OR
c) 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?
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 (i) the square of current (I2)
(ii) the resistance (R) of the conductor and
(iii) 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.
&
a) List two properties of heating elements.
b) List two properties of electric fuse.
c) 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 accidentally produced high currents.
OR
c) 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?
(ii) the resistance (R) of the conductor and
(iii) 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.
&
a) List two properties of heating elements.
b) List two properties of electric fuse.
c) 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 accidentally produced high currents.
OR
c) 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?
Updated On: Jan 13, 2026
Show Solution
Solution and Explanation
The heating effect of electric current occurs when all electrical energy is converted into heat energy in a purely resistive circuit. The heat produced (H) is calculated using the formula H = I²Rt, where I is the current, R is the resistance, and t is the time. Devices such as electric irons, heaters, and fuses operate based on this principle.
a) Properties of Heating Elements:
1. High resistivity: Materials like nichrome are used for their high electrical resistance, which generates more heat.
2. High melting point: These elements must tolerate high temperatures without melting or deforming.
b) Properties of an Electric Fuse:
1. Low melting point: The fuse wire melts readily when the current surpasses its safe limit.
2. Thin wire construction: Designed to interrupt the circuit during excessive current flow, thus protecting electrical devices.
c) Operating Principle of an Electric Fuse:
An electric fuse functions on the principle of the heating effect of electric current.
Explanation:
When excessive current flows, the heat generated (H = I²Rt) in the thin fuse wire increases. Due to its low melting point, the fuse wire quickly melts, breaking the circuit. This action disconnects the power supply, safeguarding connected appliances from damage caused by high current or short circuits.
OR
c) Given Data:
Power (P) = 1100 W
Voltage (V) = 220 V
Calculation of Current (I):
Using the formula P = VI, the current is calculated as: I = P / V = 1100 / 220 = 5 A.
Behavior of a 5 A Fuse under 5 A Current:
- The circuit draws exactly 5 A.
- A 5 A fuse is designed to melt when the current exceeds 5 A.
- As the current is at the rated limit, the fuse might not blow immediately but could melt due to heat buildup from prolonged use or a slight increase in current.
Conclusion:
While the fuse may endure the current for a brief period, it risks melting if there is a minor overload or sustained operation at its limit.
a) Properties of Heating Elements:
1. High resistivity: Materials like nichrome are used for their high electrical resistance, which generates more heat.
2. High melting point: These elements must tolerate high temperatures without melting or deforming.
b) Properties of an Electric Fuse:
1. Low melting point: The fuse wire melts readily when the current surpasses its safe limit.
2. Thin wire construction: Designed to interrupt the circuit during excessive current flow, thus protecting electrical devices.
c) Operating Principle of an Electric Fuse:
An electric fuse functions on the principle of the heating effect of electric current.
Explanation:
When excessive current flows, the heat generated (H = I²Rt) in the thin fuse wire increases. Due to its low melting point, the fuse wire quickly melts, breaking the circuit. This action disconnects the power supply, safeguarding connected appliances from damage caused by high current or short circuits.
OR
c) Given Data:
Power (P) = 1100 W
Voltage (V) = 220 V
Calculation of Current (I):
Using the formula P = VI, the current is calculated as: I = P / V = 1100 / 220 = 5 A.
Behavior of a 5 A Fuse under 5 A Current:
- The circuit draws exactly 5 A.
- A 5 A fuse is designed to melt when the current exceeds 5 A.
- As the current is at the rated limit, the fuse might not blow immediately but could melt due to heat buildup from prolonged use or a slight increase in current.
Conclusion:
While the fuse may endure the current for a brief period, it risks melting if there is a minor overload or sustained operation at its limit.
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