Adevice that creates a potential difference in an electric circuit is a(n)
a. insulator
b. voltage source
c. conductor
d. circuit

B. Voltage source

Voltage is the same as potential difference and a voltage source's function is to create a potential difference to allow current to flow.
          
                         - AS Level Student studying physics

Aform of energy that is reflected or emitted from objects in the form of electrical and magnetic waves that can travel through space. there are many forms of  electromagnetic  energy including gamma rays, x rays, ultraviolet radiation, visible light, infrared radiation, microwaves and radio waves.