How does an Electric Car Work?

All cars are energy conversion devices - converting potential energy stored in the fuel to the kinetic energy to drive the wheels. In a conventional vehicle, the fuel is petrol or diesel. When the fuel is mixed with oxygen and burned inside the Internal Combustion Engine  (ICE), it releases the energy locked in the hydrocarbons of the fuel as heat, which pushes the pistons to turn the wheels of the car.
  The burning process produces a number of chemical compounds like oxides of nitrogen,  sulphur, carbon dioxide etc. which are released to the environment through the tailpipe. These have adverse effect on the environment  (global warming) and on human health.
  The workhorse of an electric vehicle is its electric motor. It converts the chemical energy stored in the battery to mechanical energy to turn the wheels of the car. The process takes place electrochemically, without any burning of the fuel and hence no emission of any kind. Thus, an electric car is considered "clean".
  The principle of an electric motor is simple. Place a copper wire in a magnetic field and pass an AC current through it. The AC current induces a varying magnetic field in the copper due to which it experiences a force or torque. If the copper wire is in the form of a loop,then the two sides of the loop, which are at right angles to the external magnetic field experience force in the opposite directions, making the loop rotate. Attach a shaft to the loop, you have a rotating axle.
  In an actual electric motor, the rotating part is the rotor  (also called armature). Rotor has conducting coils. It is enclosed in a stator, which carries a magnet. When electric current flows through the rotor coils, the induced magnetic field interacts with the stator magnetic field to produce a torque.
  The rotor also carries a commutator, a device to reverse the direction of the current flow in the rotor to flip the induced magnetic field with respect to the stator magnetic field. This keeps the rotor from getting locked in one position but rotating continously as long as the current is flowing through it. This power is transferred to the drive wheel to drive the car. Both AC and DC motors can be used.
  One of the biggest differences between a petrol vehicle and an electric vehicle has to do with the drive train that is the transmission, gear and clutch assembly. A petrol car has a multiple speed gearbox and a clutch to engage them while driving. This is because most internal combustion engines cannot operate below about 750 RPM, which is quite high to start a car from standstill. So a step-down gear is required to adopt the high speed engine to the stationary drive wheel.
  Secondly, the range of efficient operating RPM of an ICM is very narrow between 2000 and 4000 RPM. So, a multiple gear system is required to convert this narrow power range of the engine to a wide range of vehicle speeds.
  The situation is quite different in an electric motor. First, it delivers maximum usable steady torque, right from the lowest RPM at the start to as high as 20,000 RPM. This range comfortably covers all the possible speed ranges of the car, including the start from standstill. So, instead of packing the car with a multiple gearbox, vehicle designers pick out a transmission with just one gear ratio that provides a good compromise for acceleration and top speed.