Polarity of EMF induced in open circuits

Yes lens law is used to determine direction of current whether it is clockwis or anticlockwise direction with respect to observer

If the magnetic field is uniform, you will need to create motion in the rod to create induced current and direction of the induced current can be found by Fleming's right hand rule. The end from which current will flow will have the higher potential.

If the magnetic field is circular and the rod passes through the centre of it and the magnetic is changed, then use the right hand thumb rule where the curl of your fingers of your right hand would be in the direction of magnetic field and the thumb will give you the direction of current. The end from which current will flow will have the higher potential.

At the instant the circuit is opened and current ceases to flow, the voltage will increase appreciably at the open cct.,initially in the same direction, then will decay in an oscillatory fashion within a microsecond to the value of the source voltage. Magnetic energy around the wire is converted to potential energy expressed as voltage. This is why you often see sparks in low voltage cct's. when current is interrupted. Google Lenz's law. 400 volts is generated across the points or transistor in the primary cct. of your petrol car ignition,the ignition coil with a 60:1 turns ratio multiplies this 400V to: 60 by 400 = 24 kV, for your spark plug's