Discussion
A solenoid is 1m long and 3 cm in mean diameter. It has five layers of windings of 100 turns each and carries a current of 5A. What is the magnetic field at its centre?
Answer: B
The field at the centre is \(0.314 \times 10^{-2}\) T.
For a long solenoid the field inside is \(B = \mu_{0} n I\), where n is the number of turns per metre. Five layers of 100 turns on a 1 m length give n = 500 turns per metre; the 3 cm diameter does not enter the long-solenoid formula.
\[ \begin{aligned} B &= 4\pi \times 10^{-7} \times 500 \times 5 \\ &= 3.14 \times 10^{-3}\ \text{T} \\ &= 0.314 \times 10^{-2}\ \text{T} \end{aligned} \]
\(3.14 \times 10^{-2}\) T and \(31.4 \times 10^{-2}\) T have the right digits but the wrong power of ten (10 and 100 times too large), and \(2.5 \times 10^{-3}\) T does not follow from \(\mu_{0} n I\) with these values.
Post your comment
Please log in or register to post a comment.
Examination Categories
- SSC Exams
- Banking Exams
- Teaching Exams
- Civil Services Exams
- Railways Exams
- Engineering Recruitment Exams
- Defence Exams
- State Government Exams
- Police Exams
- Insurance Exams
- Nursing Exams
- Other Government Exams
- NRA CET
- PG Entrance Exams
- Campus Placement
- MBA Entrance Exams
- CUET and UG Entrance
- Judiciary Exams
- Regulatory Body Exams
- Software Development