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how is flemings right and left hand rule different??

According to Fleming's left-hand rule:Hold the forefinger,the center finger and the thumb of left hand at right angles to one another. Adjust fingers in such a way that the forefinger points in the direction of magnetic field and center finger points in the direction of current,then the direction in which the thumb points,gives the direction of force acting on the conductor.

According to Fleming's right hand rule:Hold the thumb,the forefinger and the center finger of right hand at right angles to one another. Adjust fingers in such a way that forefinger points in the direction of magnetic field,the thumb points in the direction of motion of conductor,then the direction in which center finger points,gives the direction of induced current in the conductor.

From the above we see that the left hand rule determines the direction of force acting on a current carrying wire placed in a magnetic field,whereas right hand rule gives the direction of induced current produced in a straight conductor moving in a magnetic field. 

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Fleming's left-hand rule is used for electric motors, while Fleming's right-hand rule is used for electric generators.

Separate hands need to be used for motors and generators because of the differences between cause and effect.

In an electric motor, the electric current and magnet field exist (which are the causes), and they lead to the force that creates the motion (which is the effect), and so the left hand rule is used. In an electric generator, the motion and magnetic field exist (causes), and they lead to the creation of the electric current (effect), and so the right hand rule is used.

For example, many types of electric motors can also be used as electric generators. A vehicle powered by such a motor can be accelerated up to high speed by connecting the motor to a fully charged battery. If the motor is then disconnected from the fully charged battery, and connected instead to a completely flat battery, the vehicle will decelerate. The motor will act as a generator and convert the vehicle's kinetic energy back to electrical energy, which is then stored in the battery. Since neither the direction of motion nor the direction of the magnetic field (inside the motor/generator) has changed, the direction of the electric current in the motor/generator has reversed. This follows from the second law of thermodynamics. The generator current must oppose the motor current, and the stronger current outweighs the other to allow the energy to flow from the more energetic source to the less energetic source.

The rule for motors can be recalled by remembering that "motors drive on the left in Britain". The rule for generators can be recalled by remembering that either the letter "g" or "r" is common to both "right" and "generator".
 

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1) Fleming's left hand rule is used to find the direction of magnetic force acting on a charged particle moving in a magnetic field, or a current carrying conductor kept in a magnetic field.

2) Fleming's right hand rule is used to find the induced current in a coil encountering a change in a magnetic flux with time.

so, the rules are different and used in different contexts. 

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