Processor speed in laptops were slower?

hey i am just wondering 

Why Processors in laptops were slower then desktop

I see there is laptop with AMD A4 chip with 1.5 GHz
same chip in desktop its 3.2

so Whats deal what i am mising

both has 4 GB ram and everything same?

I see this over intel too please need advice as cheap laptop needed for collage..

Laptops run their CPUs at lower clockspeeds both to conserve battery life and reduce heat output.

laptop processors are clocked lower because of heat generation. Desktops have much larger fans and heatsinks compared to laptops which have very small fans and heatsinks. Plus they need to be more energy efficient to run off a battery. Where a desktop processor may use 85 watts of power, a laptop processor needs to use 30 watts to maximize battery life.

2 main reasons: Reduce heat output and power consumption.

Same reason why notebook GPUs run slower than their desktop counterparts.