Question

The end-use efficiency of burning coal to power a light bulb is barely 1%. What does this mean, and what factors are likely to be contributing to this low number?

Answer 1

The end-use efficiency of burning coal to power a light bulb is barely 1 %, it means that if 100 J of energy is produced by burning coal then only 1 J of useful energy is given by the bulb in form of light. There are a lot of factors contributing to this

1) The heat energy given by the coal is used up in heating water to convert it to steam so not the complete energy of coal is converted to internal energy of steam due to losses of heat by conduction, convection and radiation.

2) The super energy strikes the turbine blades and does mechanical work to rotate the turbine, again nit 100% of steam's internal energy is converted to mechanical work as some energy is lost due to frictional and other losses.

3) When the turbine rotates it rotates the armature coil in a magnetic field and electric current is produced, again due to armature losses, hysteresis losses the amount of electrical energy produced is less than the mechanical energy supplied.

4) As the current is transmitted through transmission lines, due to sufficient resistance of transmission lines, a lot of energy is wasted as heat energy (I²R) in the resistance wires.

5) Energy is lost in transformers kept both at the transmitting and receiving stations.

6) The bulb has a very high resistance so bulb also dissipates a huge amount of energy in form of heat produced due to resistance,