Construction: 1. It consists of evacuated glass bulb having cathode (K) and anode (A). 2. The semi cylindrical cathode coated with photosensitive material from inner side. 3. The anode is platinum rod. 4. The cathode is connected to negative terminal of battery and anode is connected to positive terminal of battery.
Working: When light of suitable frequency is allowed to fall on cathode it emits Photoelectrons. These photoelectrons are attracted by anode. The photoelectric current flows through the circuit &millimeter shows the deflection.