Physics Chapter on Magnetic Fields and Relays

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Questions and Answers

What happens to the magnetic field strength around a straight wire when the current decreases?

  • The magnetic field strength increases.
  • The magnetic field strength decreases. (correct)
  • The magnetic field direction reverses.
  • The magnetic field strength remains constant.

What happens to the magnetic field lines around a straight wire when the current increases?

  • The magnetic field lines become closer together. (correct)
  • The magnetic field lines remain the same distance apart.
  • The magnetic field lines disappear.
  • The magnetic field lines become further apart.

How can the strength of the magnetic field inside a solenoid be increased?

  • By decreasing the number of turns in the solenoid.
  • By using a ferromagnetic core with a lower permeability.
  • By decreasing the current flowing through the solenoid.
  • By increasing the current flowing through the solenoid. (correct)

Which of the following statements is TRUE about permanent magnets?

<p>Permanent magnets can be created by solidifying ferromagnetic metal in strong magnetic fields. (B)</p> Signup and view all the answers

In a current-carrying solenoid, where is the magnetic field strongest?

<p>At the center of the solenoid. (B)</p> Signup and view all the answers

What are the two factors that directly affect the strength of the magnetic field around a current-carrying solenoid?

<p>The number of turns in the solenoid and the current flowing through it. (A)</p> Signup and view all the answers

What is the main purpose of a relay in a circuit?

<p>To control a large current with a smaller current. (C)</p> Signup and view all the answers

What happens to the iron armature in a relay when current flows through the coil?

<p>It is attracted to the soft iron core. (C)</p> Signup and view all the answers

Flashcards

Magnetic field strength around a wire

The strength of the magnetic field around a current-carrying wire is inversely proportional to the distance from the wire. The closer you are to the wire, the stronger the magnetic field.

Current and magnetic field strength

Increasing the current flowing through a wire increases the strength of the magnetic field around it.

Magnetic field inside a solenoid

The magnetic field inside a solenoid is stronger than the field outside. This is because the field lines are more concentrated inside.

Factors affecting solenoid field strength

The magnetic field strength inside a solenoid can be increased by increasing the number of turns in the coil or by increasing the current flowing through it.

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What is a relay?

A relay is an electrical switch that uses an electromagnet to control the flow of current in another circuit.

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How a relay works

When current flows through the coil of a relay, the electromagnet is activated, attracting an armature and closing the contacts in the main circuit. This allows current to flow through the main circuit.

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Why use a relay?

Relays are useful for controlling large currents from a separate circuit, as they can handle high power without being directly connected to the main circuit.

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Applications of Relays

A relay can be used to control multiple circuits with a single control signal. It can act as a 'remote switch' allowing you to turn on or off circuits from a distance.

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Study Notes

Variation of Magnetic Field Strength

  • The strength of a magnetic field around a current-carrying wire decreases as the distance from the wire increases.
  • Increased current leads to a stronger magnetic field, field lines becoming closer together.
  • The magnetic field direction reverses when the current direction changes.
  • Inside a solenoid, the magnetic field is stronger than outside, because field lines are closer together.
  • A larger current or more turns in the solenoid creates a stronger field.

Applications of the Magnetic Effect of a Current: Relays

  • A relay is a switch based on an electromagnet principle.
  • It's useful for controlling a separate circuit (especially if the current is high).
  • In a typical relay (pictured), current in the coil magnetizes the soft iron core, attracting the L-shaped armature.
  • This closes contacts, completing the second circuit, effectively "energizing" or turning it on.

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