Answer:
0.18216 T
Explanation:
N = Number of turns = 219
A = Area = 
r = Radius = 1 cm
= Angular speed = 
Maximum emf is given by

The strength of the magnetic field is 0.18216 T
As we know that gravitational potential energy is given by

here we have
m = mass = 120 kg

h = height = 8.2 m
now from above formula


so above is the gravitational potential energy of the couch
A direct-current (DC) generator is a rotating machine that supplies an electrical output with unidirectional voltage and current. ... The field is produced by direct current in field coils or by permanent magnets on the stator. The output, or armature, windings are placed in slots in the cylindrical iron rotor.