(a) Right hand thumb rule is used to determine the direction of magnetic field around the straight conductor carrying current. It states that, if the thumb of the right hand represents the direction of the current flow, the rest of the curled fingers determine the direction of the magnetic field lines around it.(b) Fleming's left hand rule is used to find the direction of force experienced by a current carrying straight conductor placed in a magnetic field which is perpendicular to it.
Fleming's left-hand rule states that, if the thumb, forefinger and middle finger are spread perpendicular to each other. Then if the thumb represents the direction of force then the Forefinger represents the direction of the magnetic Field and the middle finger will represent the direction of the current.