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1. [for something] to turn itself on. Exactly at midnight, the lights switched on. The radio switched on early in the morning to wake us up.
2. Sl. [for someone] to become alert or excited. The wild music made all the kids switch on and start to dance. About midnight, Ed switches on and becomes a real devil.
switch something on
to close an electrical circuit that causes something to start functioning or operating. Please switch the fan on. I switched on the fan.
Produce as if operating by a control, as in She switched on the charm as soon as he walked in. [Mid-1900s] Also see switch off.
To activate something using a switch: We switched on the lights and entered the room. I switched the fan on to cool down the kitchen.
1. in. to come alive. She saw her child and immediately switched on.
2. in. to become modern and participate in current fads and events. Most kids I know switched on when they went to high school.