Key Concepts
- 1Fleming's Left vs Right Hand Rule?
- 2Motor vs Generator?
Important Formulas & Facts
Left Hand: Motor (force on current in magnetic field). Forefinger=B, Middle=I, Thumb=Force. Right Hand: Generator (induced current). Thumb=Motion, Forefinger=B, Middle=Induced current.
Motor: Electrical→Mechanical energy. Uses split ring commutator. Current input. Generator: Mechanical→Electrical energy. AC uses slip rings, DC uses commutator. Current output.
Must-Know Questions
Q1State Fleming's left-hand rule.
Fleming's Left-Hand Rule: Stretch the thumb, forefinger, and middle finger of the left hand mutually perpendicular to each other. If the forefinger points in the direction of the magnetic field (B) and the middle finger points in the direction of current (I), then the thumb points in the direction of the force (F) on the conductor. This rule is used to find the direction of force on a current-carrying conductor placed in a magnetic field, and is the principle behind electric motors.
Q2What is electromagnetic induction?
Electromagnetic induction is the phenomenon of generating an electric current (EMF) in a conductor by changing the magnetic field around it. Discovered by Michael Faraday. When a conductor moves in a magnetic field, or when the magnetic field around a conductor changes, an EMF (and hence current) is induced in the conductor. This is the principle behind electric generators and transformers.
Q3What is the function of a split ring (commutator) in an electric motor?
The split ring commutator reverses the direction of current in the coil every half rotation. This ensures that the coil continues to rotate in the same direction. Without the commutator, the coil would rotate half a turn and then reverse, just oscillating back and forth.
Q4Name the rule used to find the direction of induced current.
Fleming's Right-Hand Rule is used to find the direction of induced current (in generators). Stretch the thumb, forefinger, and middle finger of the right hand perpendicular to each other. Thumb = direction of motion, Forefinger = magnetic field, Middle finger = induced current.
Q5What is a solenoid? How does it behave like a bar magnet?
A solenoid is a coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder. When current flows through a solenoid: 1. It produces a uniform magnetic field inside (similar to a bar magnet). 2. One end acts as North pole and the other as South pole. 3. The magnetic field inside is strong and uniform (parallel lines). 4. The field outside is similar to a bar magnet (curved lines from N to S). 5. Inserting a soft iron core inside makes it an electromagnet (much stronger). The polarity can be determined by the right-hand thumb rule: curl fingers in the direction of current, thumb points to North pole.
Practice Magnetic Effects of Electric Current
Reinforce what you just revised with practice questions