Answer:
B. I, III and IV
Step-by-step explanation:
The strength of the magnetic field generated by a solenoid is given by the following formula:
B = μ₀NI/L
where,
B = Magnetic Field
μ₀ = Permeability of Free Space
N = No. of Coils
I = Current Magnitude
L = Length of Coil
Strength is also directly proportional to size of the core.
So, to increase the magnetic field strength we can:
1- The number of Loops
2- Increase the amount of Current (for same length)
3- Decrease the length (for same number of loops)
4- Increase Size of Core
So, the correct answer is:
B. I, III and IV