Magnetic Effects of Electric Current
Subject: General Science
Sample Practice Questions
Question 1: What is the unit of magnetic field strength named after Oersted?
- Tesla
- Oersted
- Gauss
- Weber
Explanation: The unit of magnetic field strength is named the 'oersted' in honor of Hans Christian Oersted for his pioneering work in understanding electromagnetism.
Question 2: Why don't two magnetic field lines intersect each other?
- Because they repel each other
- Because they attract each other
- Because at the point of intersection, the compass needle would point in two directions
- Because magnetic field lines are always parallel
Explanation: If two field lines intersected, it would mean that at the point of intersection, the compass needle would point towards two directions, which is not possible.
Question 3: At the time of short circuit, the current in the circuit:
- Reduces substantially
- Does not change
- Increases heavily
- Varies continuously
Explanation: During a short circuit, the live wire and neutral wire come into direct contact, causing the current to increase heavily. This can damage appliances unless a fuse breaks the circuit.
Question 4: What is the direction of force on a proton moving in a magnetic field?
- Always in the direction of motion
- Perpendicular to both velocity and magnetic field
- Always opposite to the direction of motion
- In the direction of the magnetic field
Explanation: The force on a charged particle moving in a magnetic field is perpendicular to both the velocity (direction of motion) and the magnetic field. This is given by Fleming's left-hand rule.
Question 5: What is the direction of magnetic field lines outside a bar magnet?
- From south pole to north pole
- From north pole to south pole
- From east to west
- From west to east
Explanation: By convention, magnetic field lines emerge from the north pole and merge at the south pole outside the magnet. Inside the magnet, the direction is from south to north.
Question 6: Which of the following can change when a proton moves freely in a magnetic field?
- Mass
- Speed
- Velocity
- Both B and C
Explanation: A magnetic field can change the direction of motion of a charged particle (velocity), but not its speed or mass. Since velocity changes, momentum (mass × velocity) also changes.
Question 7: Who discovered that a compass needle gets deflected when an electric current passes through a nearby metallic wire?
- Andre-Marie Ampere
- Hans Christian Oersted
- Michael Faraday
- Georg Simon Ohm
Explanation: Hans Christian Oersted accidentally discovered in 1820 that a compass needle got deflected when an electric current passed through a metallic wire placed nearby. This showed that electricity and magnetism were related phenomena.
Question 8: How does the magnetic field produced by a current-carrying wire change with distance?
- It increases with distance
- It decreases with distance
- It remains constant
- It becomes zero
Explanation: The magnetic field produced by a given current in a conductor decreases as the distance from it increases. This is why the concentric circles become larger as we move away from the wire.
Question 9: What does the closeness of magnetic field lines indicate?
- The magnetic field is weaker
- The magnetic field is stronger
- The magnetic field is zero
- The magnetic field is uniform
Explanation: The relative strength of the magnetic field is shown by the degree of closeness of the field lines. The field is stronger where the field lines are crowded.
Question 10: What is the shape of magnetic field lines around a straight current-carrying conductor?
- Straight lines
- Concentric circles
- Ellipses
- Parabolas
Explanation: The magnetic field lines around a straight current-carrying conductor are concentric circles centred on the wire, as observed when iron filings are sprinkled around it.