Science Olympiad Test: Magnetic Effects of Electric Current- 2 - Class 10 MCQ

• Commercial electric motors require large magnetic field which they obtain using a solenoid having large number of turns with a soft iron core at the centre.
• The magnetic field due to solenoid is
  B α nI
• Large number of turns (n) provide large magnetic field at the centre.
• A permanent magnet is a weak magnet which is unable to provide the large magnetic field require for commercial applications.

5 Hz means that the bulb glows only 5 times in a second. For the bulb  to appear as glowing continuously, the frequency of AC should be at least 16 Hz.

The magnetic field for a point inside a long straight current-carrying solenoid is double then for a point situated at one of its ends.

The magnitude of induced emf is given by,

Which depends upon number of turns (N), magnetic field intensity (B) which depends upon medium, rate of change of area (ds/dt) which depends upon insertion speed of magnet. It is independent of resistance of coil.

In India the frequency of AC is 50 Hz which means that AC changes its polarity after 1/100 s
(i.e., 100 times per second) as it complete one cycle i.e., from + ve to –ve and from –ve to + ve 1/50 sec.

• The fuse wire is made up of Sn (tin) and Pb (lead) alloy because of its high resistance and low melting point. 
• The tin and lead alloy is a eutectic composition(low melting point composition) consisting of 62% tin plus 38% lead.
• Melting point of this alloy is 1830C
• In case of short circuit when a high current flows through the fuse wire then due to overheating, the fuse wire melts and breaks the circuit.
• As the circuit breaks, the household electrical components are saved from damage due to the high current.

The two magnetic fields, each due to the semicircular segment of the coil through A and B, assist each other as we move towards the centre of the coil.

Magnetic field ∝ 1/r
When r doubles (10 cm to 20 cm), the magnetic field becomes half (2 T → 1 T)

It has been found that Force (F) acting on a current-carrying conductor placed on a magnetic field, in a direction perpendicular to the direction of the magnetic field, is directly proportional to the current, length of the conductor and magnitude of the field F = k I l B. In SI units, constant k = 1 Also, Force acting on a suspended mass = mg ⇒ mg = I l b

No force acts on a charged particle when it is moving either parallel (0°) or antiparallel (180°) to the magnetic field. In all other cases, the charged particle experience a force.

The direction of the induced current varies once every half revolution when a rectangular coil is rotated in a magnetic field. As a consequence, the current in the coil continues to flow in the same direction.

15 Amperes current rating circuits are used for higher power consumption sources that have a high power rating. It includes an air conditioner, geysers and iron box.

Potential difference between a live wire and a neutral wire in a domestic circuits it 220 V and the frequency of an AC is 50 Hz.

When Magnet moves with its North pole towards the coil, emf is induced in the coil as the magnetic flux through the coil changes. So, when seeing from magnet side the direction of induced current appears to be Anticlockwise.