Given:
- Side of the square coil (l) = 20 cm = 0.2 m
- Number of turns in thousands (N) = 1000
- Rotational speed (n) = 60 revolutions per minute
- Magnetic field strength (B) = 100 T

To find:
The maximum emf developed across the coil.

Solution:

Step 1: Calculate the angular velocity (ω)
The angular velocity is the rate at which the coil rotates in radians per second. It can be calculated using the formula:

ω = 2πn

Where,
n = rotational speed in revolutions per minute

Substituting the given value:
ω = 2π * 60 = 120π rad/s

Step 2: Calculate the magnetic flux (Φ)
The magnetic flux through the coil can be calculated using the formula:

Φ = B * A

Where,
B = magnetic field strength
A = area of the coil

Since the coil is square-shaped, the area can be calculated as:

A = l^2

Substituting the given value:
A = (0.2)^2 = 0.04 m^2

Φ = 100 * 0.04 = 4 Tm^2

Step 3: Calculate the maximum emf (ε)
The maximum emf developed across the coil can be calculated using Faraday's law of electromagnetic induction:

ε = -N * dΦ/dt

Where,
N = number of turns
dΦ/dt = rate of change of magnetic flux

Since the coil is rotating, the rate of change of magnetic flux can be calculated as:

dΦ/dt = d(Φ*cos(ωt))/dt

Taking the derivative:
dΦ/dt = -ωΦ*sin(ωt)

Substituting the given values:
dΦ/dt = -120π * 4 * sin(ωt)

Since we are interested in the maximum emf, we can substitute the maximum value of sin(ωt), which is 1:

dΦ/dt = -120π * 4 * 1 = -480π

Now, substituting the values in the formula for ε:
ε = -N * dΦ/dt
= -1000 * (-480π)
= 480,000π T/s

Step 4: Convert the emf to volts
To convert the emf from teslas per second to volts, we use the conversion factor:

1 T/s = 1 V

Therefore, the maximum emf developed across the coil is:
ε = 480,000π V/s

Hence, the maximum emf developed across the coil is 480,000π V/s.