Why does the bulb glow, when the electric current passes through it?
A. Due to lighting effect of electric current
B. Due to magnetic effect of electric current
C. Due to chemical effect of electric current
D. Due to heating effect of electric current

Hint: When current flows in a circuit it exhibits various effects. The main effects are heating, chemical and magnetic effects. We use different types of apparatus at home based on these effects of current.

Step by step answer: In the bulb there is a thin wire, called the filament, which glows when an electric current passes through it. It is made of a tungsten wire enclosed in a glass bulb from which air has been removed. This is because air would oxidize the filament. The filament is heated up to a high temperature and becomes white hot. This glowing filament gives light.
This is the heating effect of the electric current.

Hence option (D) is correct.

Additional Information: In other options magnetic and chemical effect of current is mentioned. The magnetic effect of electric current is known as electromagnetic effect. It is observed that when a compass is brought near a current carrying conductor the needle of the compass gets deflected because of flow of electricity. This shows that electric current produces a magnetic effect.
The passage of an electric current through a conducting liquid normally causes chemical reactions and the resulting effects of this reaction are known as chemical effects of currents

Note: Students may confuse and assume that bulb glows due to lightning effect if current, but actually this lightning effect is produced because of heating effect in bulb. Heating and lighting both are observed in filament bulbs.