You can but it is not recommended.
You can plug in as many as you want but none of them will work. An "open" circuit is an electrical circuit which is not a complete circuit and therefore electricity will not flow through it. If you mean an unused circuit,which has no load on it, then the answer is 2 ea. 5 amp devices on a 15 amp circuit and 3 ea. 5 amp devices on a 20 amp circuit. The reason for this is that any circuit is not to be "loaded" more than 80% of the OCPD (circuit breaker amperage rating.
Yes, the amp rating is a measurement of the highest amp load it should carry. So a 15 amp appliance will work on a 20 amp socket but you wouldn't want to use a 20 amp appliance on a 15 amp socket.
120 15 amp service ? 210 7 amp service ?
No, the one amp fuse is the recommendation of the manufacturer of the circuit. By replacing it with a fuse five times larger will default the warranty placed on the equipment by the manufacturer. Where one amp will do no damage to the circuit, five amps could destroy the components that are connected in the circuit.
Yes
5 amp,10 amp, 15 amp, 20 amp, 25 amp, and 30 amp.
It's basically a system of circuits. The power from the mains enters through the input terminals. It's then split into various load circuits (5 amp for lighting, 13 amp for sockets , 15 amp for the immersion heater & 30 amp for cookers). Each of these circuits has it's own circuit breaker, which cuts the power to that particular circuit if the current draw exceeds the rating of the breaker.
If it is then it has a 3 or 5 amp fuse. Some are not.
In how many amps of current before blowing out. 2 amp 5 amp 10 amp 15 amp etc.
In a fault condition there would be a three fold quantity of the current on a circuit that was designed for a maximum of 5 amps. In electronic circuitry this could destroy the equipment. Also a fire is a possibility.
Current carrying capacity is different.
A 5-amp fuse is designed to fail if more than 5 amps goes through it. A 6-amp fuse does likewise with more than 6 amps. Therefore, if you replace a 5-amp fuse with a 6-amp, you might be leaving components vulnerable to damage and wiring vulnerable to overheating, which could start a fire. If you replace a 6-amp with a 5-amp, the fuse will burn out if the circuit is drawing between 5 and 6 amps.