HP Chromebook 11 G5 (Setzer) CPU speed clocked at 1.60 GHz instead of 2.48GHz (Braswell)

I own a HP Chromebook 11 G5. I’ve noticed that when it’s connected to a power source, the CPU operates at 1.60GHz. However, when it runs on battery power, the CPU’s Turbo Boost feature raises the speed to 2.48GHz. Could you explain why this happens?