Class 12 Physics — Chapter 4: MOVING CHARGES AND MAGNETISM

What you'll learn

• ▸Oersted's Discovery: Current as a Source of Magnetism
• ▸The Lorentz Force
• ▸Magnetic Force on a Moving Charge
• ▸Units and Magnitude of Magnetic Field
• ▸Magnetic Force on a Current-Carrying Conductor
• ▸Principle of Superposition for Magnetic Fields

Chapter Summary

--- PAGE 1 --- NCERT republished Chapter Four MOVING CHARGES AND MAGNETISM 4.1 INTRODUCTION Both Electricity and Magnetism have been known for more than 2000 years. However, it was only about 200 years ago, in 1820, that it was realised that they were intimately related. During a lecture demonstration in the summer of 1820, Danish physicist Hans Christian Oersted noticed that a current in a straight wire caused a noticeable deflection in a nearby magnetic compass needle. He investigated this phenomenon. He found that the alignment of the needle is tangential to an imaginary circle which has the straight wire as its centre and has its plane perpendicular to the wire. This situation is depicted in Fig.4.1(a). It is noticeable when the current is large and the needle sufficiently close to the wire so that the earth's magnetic field may be ignored. Reversing the direction of the current reverses the orientation of the needle [Fig. 4.1(b)]. The deflection increases on increasing the curre…

Practice Questions from this Chapter

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1. Explain how electricity creates magnetism. Get Solution →
2. What makes magnets stick together? Get Solution →
3. Describe how magnetic fields are used? Get Solution →
4. Who first discovered in 1820 that an electric current produces a magnetic field? Get Solution →
5. What is the SI unit of magnetic field strength? Get Solution →
6. What is the name of the force experienced by a charge q moving in the presence of both an electric field E and a magnetic field B? Get Solution →
7. According to the convention mentioned in the chapter, what does a cross symbol (⊗) represent? Get Solution →
8. A magnetic force will not act on a charged particle if the particle is... Get Solution →

Did you know?

• 💡 Oersted accidentally discovered electromagnetism during a lecture demonstration in 1820.
• 💡 Our Earth has a giant magnetic field that protects us from solar radiation.
• 💡 Migratory birds and sea turtles can sense Earth's magnetic field to navigate.
• 💡 Giant electromagnets in junkyards can lift entire cars using electric currents.
• 💡 You can never isolate a magnetic north pole or south pole; they always come in pairs.

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