Braking torque in a single phase meter refers to the torque that opposes the rotation of the meter disc when external load is applied. This torque is provided by a permanent magnet, which interacts with the eddy currents induced in the metal disc.

The braking torque can be determined by considering the factors that affect it:

1. Flux of the Permanent Magnet:
The braking torque is directly proportional to the square of the flux produced by the permanent magnet. The flux is produced by the magnet and passes through the disc, inducing eddy currents. These eddy currents interact with the magnetic field, creating a torque that opposes the rotation of the disc. The greater the flux, the stronger the interaction and the greater the braking torque.

2. Speed of the Meter:
The braking torque is also proportional to the speed of the meter. As the speed increases, the eddy currents induced in the disc also increase. This results in a stronger interaction with the magnetic field, leading to a higher braking torque. Conversely, when the speed decreases, the eddy currents decrease, resulting in a lower braking torque.

Considering both factors, the braking torque is proportional to the square of the flux of the permanent magnet and the speed of the meter. The relationship between these factors can be expressed by the equation:

Braking Torque ∝ Flux^2 × Speed

Thus, the correct answer to the given question is option 'C' - both (a) and (b). Both the flux of the permanent magnet and the speed of the meter have a direct influence on the braking torque provided by the permanent magnet in a single phase meter.

In summary, the braking torque provided by a permanent magnet in a single phase meter is determined by the square of the flux of the magnet and the speed of the meter. The greater the flux and speed, the higher the braking torque.