On UK mains (three pin) sockets, there is a plastic gate mechanism that blocks the live and neutral pin holes, the earth(ground) pin is longer and lifts the gate up as it is inserted.
What I want to know is, why are UK plugs so bloody huge? 
So that even clumsy fingered people can fit a plug to a new appliance. (We are taught this in school too.)
Why shouldn’t they be? - it’s not as if you have to fit them inside your ear or anything.
Once upon a time mercury switches were commonly used. I believe they were outlawed some time ago because of health/environmental concerns. Anyway, my grandparents home (built in the early 1930’s) has a couple of them and they only work as toggle up=on, toggle down=off no matter how they are placed in the wall box. The switch toggle has a cavity with a bead of mercury on the opposite side of the pivot point. When the switch is toggled up, the mercury rolls to the bottom of the cavity, touches the contacts located there and completes the circuit causing the lights to come on. Toggle the switch down and the cavity goes up thereby moving the mercury away from the contacts and breaking the circuit.
I discovered this many years ago when I noticed that the switch in one of their bedrooms was installed upside down. There was labeling for the on/off positions on the toggle, but they were upside down. The switch, however, still operated as up=on and down=off regardless of what the labels said.
Well, UK plugs handle a lot of current, a full 13 Amps. I am not sure what the rating of US plugs is, but I guess it’ll be about half that.
They are very safe - they have an internal fuse and are difficult to pull out by accident. As pointed out by Mangetout, modern versions of the socket has an internal gate arrangement that helps to prevent accidents such as inquisitive children poking something in.
Switches in India follow the UK standard. All switches are on when down and off when up.
Except, as mentioned, circuit breaker switches. These are on when up and off when down.
Two-way switches, ofcourse, are on both ways and off both ways. So there’s a similarity between US and UK switches 
Not so!
Here’s some American 20A receptacles
My tablesaw has its own 20A circuit, complete with an outlet that looks like the second one down on that page. It has the T-shaped left slot, like the picture. (and no, this doesn’t mean one prong is T shaped. Rather, on some devices, one prong is horizontal.)
Hmmm.
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Most US electrical sockets are on circuits with 15 amp breakers; many go up to 20.
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US sockets do not have the gate mechanism, although one can buy them (for households with children).
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Smaller plugs are more convenient; for example, when a socket is hidden behind furniture.
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While most sockets in the US are “always on,” many homes contain at least one switchable socket for lamps and such; these sockets are wired to a wall switch. I believe I have seen the safety switch shown in r_k’s link in home stores, but they are not common.
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Yes, rocker switches are very common in theUS, though not as common as lever switches. There are also push buttons, dimmer knobs, touch plates, and slider switches.
[smirk] Our appliances come with, wait for it, plugs already attached![/smirk]
Well, except for thinks like electric clothes dryers and electric ranges.
You really have to attach your own plugs when you purchase appliances?
Not any more; they have to have a plug fitted (containing the right size fuse) by law - it’s been like that for years.
Do American mains plugs contain a fuse?
Very, very rarely – I’ve seen things like that on christmas lights.
That will be one reason that UK 3 pin plugs are larger then.
yep, that’s the reason
no
Not when you purchase them, but if you 'amend ’ them, or plan to have hidden wires.
I have a cabinet where I drilled small holes throiuugh the back to take the wiring for the TV, DVD player, video, stereo etc…, and all the plugs had to be removed and refitted to enable the wires to feed through, keeping the holes in the furniture to a minimum.
Can you remove the plug on American appliances, and refit?
The plugs are almost always molded on to the cord, but they can be cut off and a replacement plug can be fitted. This is what we would do if we wanted to minimize the hole that the cord goes through. I once bought some light fixtures that were meant to be installed inside cabinets, and they had removable plugs for this reason.
I am not sure that UK plugs are really all that big.
I am not sure about US designs, but UK plugs have the wire comming out parallel to the wall. Pulling on the cable will not get the plug out easily. There are chunky UK plugs that are designed so that you can get a good finger-grip on the plug to pull it out easily. This type also is cheap and has bags of space inside so that it is easy to wire up yourself.
However, there are more compact UK plugs available. The most compact are slim moulded on type.
All UK plugs are fused.
Most UK sockets are switched - they don’t have to be.
My ring-main at home is rated at 30A. I think this is pretty standard. To protect the ring-main, every outlet with more than two sockets must itself be fused.
I forgot to mention that UK voltage is 230V so a UK 13A plug can draw nearly 3 kW whereas even a 20A US plug is drawing about 2.4kW.
I thought the standard for the ring-main was 15A, with a separate 30A circuit for the cooker and electric shower (etc) - I’m pretty sure that’s how my house is wired.
Mangetout: On a UK domestic ring main it is usual to have 15A wire, but being a ring, this can safely take 30A, so there’ll be 30A fuse in the fuse-box. Of course, not all houses have a ring main and in older or much altered properties one can find all sorts of strange arrangements.