Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Magnets have two poles: North () and South (). Like poles repel, and opposite poles attract.
Magnetic materials include Iron (), Nickel (), and Cobalt (). Steel is an alloy containing iron and is used to make permanent magnets.
Magnetic field lines represent the direction and strength of a magnetic field. They always point from North () to South ().
The density of field lines indicates field strength; where lines are closest together (at the poles), the field is strongest.
Induced magnetism occurs when a magnetic material is placed in a magnetic field and becomes a magnet itself. This magnetism is usually temporary.
Hard magnetic materials (e.g., Steel) are difficult to magnetize but retain their magnetism. Soft magnetic materials (e.g., Iron) are easy to magnetize but lose it quickly.
An electromagnet is a temporary magnet produced by an electric current flowing through a coil of wire (a solenoid).
The strength of an electromagnet can be increased by: increasing the current (), increasing the number of turns in the coil (), or adding a soft iron core.
The Right-Hand Grip Rule: If you wrap your right hand around a solenoid with fingers in the direction of current (), your thumb points toward the North pole ().
📐Formulae
\frac{V_p}{V_s} = rac{N_p}{N_s}
💡Examples
Problem 1:
A student wants to increase the strength of an electromagnet. If the current is currently and the coil has turns, calculate the new relative strength if the current is doubled and the turns are tripled.
Solution:
The strength is proportional to . Initial strength . New current and new turns . New strength .
Explanation:
Since the strength of an electromagnet is directly proportional to both the current () and the number of turns (), the total factor of increase is times the original strength.
Problem 2:
A transformer is used to step up voltage. The primary coil has turns and a voltage of . If the secondary coil has turns, calculate the secondary voltage .
Solution:
Explanation:
Using the transformer equation , we can solve for the unknown voltage by cross-multiplying and isolating .
Problem 3:
Identify the polarity of an electromagnet if the current enters the solenoid and flows clockwise when viewed from the right end.
Solution:
The right end acts as a South () pole.
Explanation:
According to the clock rule, if the current flows in a clockwise direction, that end of the solenoid behaves as a South pole. Conversely, an anti-clockwise current indicates a North pole.