Question

Complete the sentence. The leakage flux of a toroid is less because
A. It is asymmetrical
B. It has an open-loop core
C. It is symmetrical
D. It has a straight core

Answer 1

The toroid is a surface of revolution with a hole in the middle; it is a hollow ring on which a large number of turns of a wire are closely wound. In other words, it is a solenoid bent into a circular shape to close on itself.

Complete step by step answer:

The toroid is circular in shape with a hole in the middle and wire coiled around it closely wound to form a symmetrical structure. It is very similar to solenoid only round in shape.
Leakage flux is non-desired flux leaked from an electromagnetic system due to design flaws, for example, a solenoid of infinite length with not have any leakage flux but since it is not practically possible to make an infinite length solenoid, therefore, some leakage flux is observed outside the solenoid.
This is minimal in the case of a toroid as the toroid is ring-shaped and it is physically possible to construct a toroid close to the ideal toroid. This round shape of the toroid is the reason that it has minimal leakage flux even compared to a solenoid.
Hence, the correct option is that the reason for the leakage flux of a toroid is due to the fact that it is symmetrical.
Therefore the correct option is C.

Note: If we observe the other options available, we see that the first option states that - It is asymmetrical; this is incorrect because the structure of toroid is symmetrical.
The next option states that it has an open-loop core, the core of a toroid is doughnut/ring-shaped, and hence it is a closed-loop and not open-loop core. Therefore, this option is also incorrect.
The last option is that it has a straight core. This is absolutely incorrect as the toroid has a ring-shaped core. It is the solenoid that has a straight core, not a toroid.
Therefore, all the other options state incorrect points about the toroid.
Additional Information: Both the solenoid and the toroid are cases of high symmetry where the Ampere’s Circuital Law can be applied conveniently. In the case of a toroid and an infinite solenoid, we notice that the magnetic field inside and outside the toroid is zero. The magnetic field outside a long solenoid approaches zero, the field observed experimentally is due to leakage flux.