Moving coil galvanometer working | Moving charges & magnetism | Physics | Khan Academy

Summary

This video explains the working principle of a moving coil galvanometer, which uses a current-carrying coil that acts like a magnet within a magnetic field. The torque produced causes the coil to rotate, indicating current strength. Challenges such as continuous rotation and the coil's inability to return to zero are addressed through counter torques provided by coil springs. To achieve a linear relationship between current and deflection, a radial magnetic field is created using concave pole pieces and a soft iron core, ensuring accurate and proportional measurements.

Takeaways

• 😀 A moving coil galvanometer uses current to generate a magnetic field, causing a coil to behave like a magnet.
• 🔄 Increasing the current through the coil increases the torque, resulting in a greater deflection of the pointer.
• ⚖️ The galvanometer must balance the magnetic torque with a counter torque to stabilize the pointer at equilibrium.
• 🔧 Coil springs provide the necessary counter torque, allowing the galvanometer to return to a resting position when current stops.
• 📏 A linear response is essential, meaning deflection should be proportional to the current passing through the coil.
• 🌀 The angle between the coil and the magnetic field affects the torque; to maintain linearity, this angle must remain constant.
• 🔍 A radial magnetic field can be created using concave pole pieces and a soft iron core to keep the angle at 90 degrees.
• 🔩 This design ensures that the magnetic field acting on the coil always produces consistent torque, leading to linear behavior.
• 📊 Ultimately, a properly designed galvanometer shows direct proportionality between current and deflection, making it effective for measurements.
• 🔄 The construction of the galvanometer, including its components and arrangement, plays a critical role in its functionality and accuracy.

Q & A

What is the basic principle of a moving coil galvanometer?

A moving coil galvanometer operates on the principle that passing current through a coil generates a magnetic field, causing the coil to behave like a magnet and experience torque when placed in an external magnetic field.

What happens when current increases in a galvanometer?

When the current increases, the torque on the coil also increases, resulting in a greater deflection of the coil, indicating a higher current.

Why does the coil in a galvanometer keep turning indefinitely if not modified?

Without modifications, the coil will continue to turn indefinitely because the torque from the magnetic field remains as long as current flows, leading to unbalanced forces.

How do coil springs improve the galvanometer's functionality?

Coil springs provide a counter torque that balances the magnetic torque, allowing the coil to stop turning at a specific angle based on the amount of current.

What is the significance of ensuring a linear response in a galvanometer?

A linear response means that the deflection of the galvanometer is directly proportional to the current, which is crucial for accurate measurements.

How does the design of the magnetic field affect the galvanometer's performance?

The design of the magnetic field, particularly by using concave pole pieces and a cylindrical soft iron core, creates a radial magnetic field that maintains a constant angle, ensuring linearity in the galvanometer's response.

What role does the angle between the magnetic field and the coil play in torque generation?

The torque generated depends on the angle between the coil (acting as a magnet) and the magnetic field; the torque is maximized when this angle is 90 degrees.

What modifications are made to ensure the galvanometer is a linear device?

To ensure linearity, the magnetic field is made radial, which keeps the angle between the field and the coil constant at 90 degrees, allowing deflection to be proportional to current.

What does it mean for the galvanometer to reach equilibrium?

Equilibrium is reached when the torque from the magnetic field equals the counter torque from the springs, stabilizing the position of the coil at a specific angle that corresponds to the current.

Why is the radial magnetic field preferred in the design of a galvanometer?

A radial magnetic field ensures that the torque remains constant regardless of the coil's position, allowing for reliable and consistent measurements of electric current.