Using Crocodile Clips programme. - select 'OPTIONS' then 'Indestructible Components' SELECT - ' Add' > Power Supplies' then 'Batteries' Then 'ADD' >'Switches' > 'Push-to-make' . SELECT 'Passive Component' > then 'Electrolytic capacitors' - Next Select "ADD" > 'SWITCHES' > 'RELAY (SPDT)'
Explore the toolbar and create the circuit shown here. This is the basic circuit that simulates the 'charging' of the capacitors on our buggy simply be pushing the 'push-to-make' switch. On the buggy there are two short metal rods on the front of the buggy onto which the contacts of a PP3 ( 9v ) battery can be placed.
To reinforce what you have learnt about capacitors and time constants, now experiment with the values of the capacitors and find out what values will give a delay of 5 seconds. Notice that once the push-to-make switch has been pressed it immediately returns to the off position. The voltage is therefore coming from the charge stored in the capacitors. Now add the motor and the 3 volt battery. Explore the menu bar to find the way to do that.
Once the capacitor circuit has been developed it might be sensible to explore the 'output' side of things - the relay and circuit that activates the motor. Explore the toolbar to add the motor and a 3v battery supply.
The motor should now be controlled by the relay's turning on and off.
What we now need to do is to replace the 'push-to-make' switch with a transistor circuit similar that used in the water detector. Using your new-found knowledge of the 'Crocodile Clips' programme find the NPN transistor you will need - and the LDR (with lamp). Connect up as shown here. Make sure you remember the symbols for these components as there are always questions in exams that require you to identify components by their symbols.
If the Capacitors were charged they would now act like a Battery - so add the battery with a push-to-make switch. The new circuit should look like this....