Do they look any different? I can not see the difference and I do not know which trains are electric and which ones are diesel. If there is any difference in appearance, what is the difference?
An electric train will have either overhead cables or a third rail which feeds the current to the traction motors. In the case of a train which draws its power from overhead cables, there is a device fixed to the roof called a pantograph which picks up the power. Typically it looks like a diamond-shaped frame or an angled arm with a bar on top which makes contact with the electric cable. Edit: Also clearly visible are the rows of masts and gantries alongside and over the track, which support the overhead wires. A diesel train is self-contained, in other words it does not rely on any external power source. Noise from an electric train is minimal. You may hear whining from the motors and a cracking or clicking sound from the switch banks and circuit breakers, but not much else. A diesel train on the other hand has a noticeable exhaust sound, which can vary from one train to another but is clearly audible and fairly loud, the exhaust is visible as it is expelled from the outlet vents, and the exhaust can also be smelt. The tang of diesel exhaust is unmistakeable. Other than that, the body design of diesel and electric trains tends to be similar, so in telling them apart you will need to look for the details as above. Edit: re Mitchey's answer, last paragraph. Mostly right, but there is one type of locomotive in use in the UK called the electro-diesel which can operate on a third rail system, or under its own power using a built-in diesel powered generator, over tracks where there is no third rail.
In some cases if nothing is actually running(engines)It is almost impossible to tell just by looking, an example of this would be the HS125 running out of Kings Cross/St Pancras which with the pantograph lowered looks exactly the same as the standard diesel powered unit. I would point out that in the UK that not all diesels are diesel electric, some were diesel mechanical ie. fed through a gearbox to the driving wheels and diesel hydraulic fed through a hydraulic pump to hydraulic motors on the driving axles.
If it has a raised pantograph on the roof (or in some cases, a slider connecting to an electric live rail next to the track), it's electric. If it emits exhaust gas, it's diesel (or steam). Rango forgot about hydrodynamic transmissions. Not all diesel trains have electric transmission, though it's used by a majority of diesel trains in the world. And some modern diesel locomotives actually have a very good noise dampening, so they are not much louder than an electric locomotive.
First off, all trains are electric, the only reason there is a diesel engine is to run a huge generator that supplies electricity for locomotive. but in a straight electric, first you would notice it is quiet and smoke free, no diesel egnines running. Second it has to have a way of getting electrictity to the motors while on the move, the most common and effective way is with overhead wires, the track will have lines directly over the center, and th elocomotives will have a device mounted on top that pushes gently upwards against the wires to conduct the electricity down into the control compartment of the locomotive. Look for the overhead device on top of the locomotive, very easy to spot.
One of the most obvious differences is that usually, (with the exception of DMU's, or Diesel Multiple Units, and railmotors, railcars, etc), is that Diesels don't have windows, except for the cab windows. Another obvious diffence is Diesels (as said above in previous answers) do not obtain power from overhead wires, or Catenary as they are called. Electric trains are a lot quieter, they don't have a sort of diesel smell about them, they accelerate faster, and they don't emmit any exhaust. Electric trains can also be pointed out easily if the Pantograph, or current collector can be seen. The Pantograph is a moveable frame on the roof of one or more carriages in an electric train that makes contact with the Catenary (electric wires above the track) and takes the power to the train, hence making it go. Electric trains can also receive electricity from a live third rail, or in some cases (such as the London Underground), 2 additional live rails (forth rail). A confusing point - Diesels can operate on track with and without Catenary, however, (overhead) electric trains can ONLY operate on track with Catenary. Likewise for thrid rail electrics, they can only operate on track with an additional live rail. Hope this helps.
