Why is spark produced in the switch off a fan when it is put off?

Why do birds fly off high tension when current is switched on?

Why does the temperature of a gas rise when it is suddenly compressed?

What is interference of light? Write two essential conditions for sustained interference pattern to be produced on the screen. Why interference pattern is not detected when two coherent sources are far apart?

Which compound is produced when ethanal is heated with dilute NaOH solution?

An electric kettle has two coils. When one of these is switched on, the water in the kettle boils in 15 minutes. When the other is switched on, the water boils in 30 minutes. In how many minutes will water boil if the coils are connected in series and switched on?