You will need:
1. Wash the coins thoroughly and dry them.
2. Roll the lemon or orange across a bench, pushing down to 'juice' the lemon.
3. Ask an adult to carefully cut two small slits in the lemon rind, fairly close together.
4. Place the coins into the slits, making sure they dont touch each other.
5. What will happen if you touch your tongue to the coins at the same time? Try other foods!
6. If you have a multimeter, try measuring the current created in the circuit.
The coins are made of two different materials... i.e. copper and zinc - not really silver! When you place two different metals apart in an acid, electricity will flow if you complete the circuit.
The saliva on your tongue is electrically conductive,
so touching the coins with your tongue completed the circuit.
The acid in the lemon allowed the Copper atoms to travel to the Zinc coin, whilst electrons from the Zinc coin travel towards the copper coin, via your tongue! You've made a simple Voltaic Cell.
Find out more about how batteries work.