Chapter 13 Magnetic Effects of Electric Current Solutions
Question - 21 : - What precaution should be taken to avoid the overloading of domestic electric circuits?
Answer - 21 : -
A few of the precautions to be taken to avoid the overloading of domestic electric circuits are as follows:
• Connecting too many devices to a single socket should be avoided
• Using too many appliances at the same time should be avoided
• Faulty appliances should not be connected to the circuit
Question - 22 : - Which of the following correctly describes the magnetic field near a long straight wire?
Answer - 22 : -
1. The field consists of straight lines perpendicular to the wire.
2. The field consists of straight lines parallel to the wire.
3. The field consists of radial lines originating from the wire.
4. The field consists of concentric circles centered on the wire.
Answer
d. The field consists of concentric circles centered on the wire.
The magnetic field near a long straight wire are concentric circles. Their centers lie on the wire.
Question - 23 : - The phenomenon of electromagnetic induction is
Answer - 23 : -
1. the process of charging a body.
2. the process of generating magnetic field due to a current passing through a coil.
3. producing induced current in a coil due to relative motion between a magnet and the coil.
4. the process of rotating a coil of an electric motor.
Answer
c. producing induced current in a coil due to relative motion between a magnet and the coil.
The phenomenon of inducing current in a coil due to the relative motion between the coil and the magnet
Question - 24 : - The device used for producing electric current is called a
Answer - 24 : -
1. generator
2. galvanometer
3. ammeter
4. motor
Answer
a. generator
The device used for producing electric current is known as generator. Generator converts mechanical energy to electric energy.
Question - 25 : - The essential difference between an AC generator and a DC generator is that
Answer - 25 : -
1. AC generator has an electromagnet while a DC generator has permanent magnet.
2. DC generator will generate a higher voltage.
3. AC generator will generate a higher voltage.
4. AC generator has slip rings while the DC generator has a commutator.
Answer
d. AC generator has slip rings while the DC generator has a commutator.
AC generators have two rings known as the slip rings while DC generators have two half rings known as the commutator. This is main difference between AC generator and DC generator.
Question - 26 : - At the time of short circuit, the current in the circuit
Answer - 26 : -
1. reduces substantially.
2. does not change.
3. increases heavily.
4. vary continuously.
Answer
c. increases heavily
When two naked wires in the circuit come in contact with each other, the amount of current flowing in the circuit increase abruptly resulting in short circuit.
Question - 27 : - State whether the following statements are true or false.
Answer - 27 : -
1. An electric motor converts mechanical energy into electrical energy.
2. An electric generator works on the principle of electromagnetic induction.
3. The field at the center of a long circular coil carrying current will be parallel straight lines.
4. A wire with a green insulation is usually the live wire of an electric supply.
Solution:
a. False
An electric motor converts electrical energy into mechanical energy.
b. True
An electric generator is a device that generates electricity by rotating a coil in a magnetic field.
c. True
A long circular coil is a solenoid. The magnetic field lines inside a solenoid are parallel straight lines.
d. False
Live wires have red insulation cover while the earth wire has green insulation.
Question - 28 : - List two methods of producing magnetic fields.
Answer - 28 : -
Following are the methods of producing magnetic fields:
• By using a permanent magnet we can produce magnetic field and it can be visualized by spreading iron fillings on a white paper and keeping a magnet beneath the paper.
• A current carrying straight conductor produces magnetic field.
• Different types of conductors such as solenoid and circular loop can be used to see the presence of magnetic field.
Question - 29 : - How does a solenoid behave like a magnet? Can you determine the north and south poles of a current–carrying solenoid with the help of a bar magnet? Explain.
Answer - 29 : - A solenoid is a long coil of circular loops of insulated copper wire. The magnetic field produced around the solenoid when the current is passed through it is similar to the magnetic field produced around the bar magnet when current is passed through it. The figure shown below shows the arrangement of magnetic fields produced around the solenoid when current is passed through it.
When the north pole of the bar magnet is brought close to the end connected to the negative terminal of the battery, the solenoid repels the battery. As like poles repel each other, we can infer that the end connected to the negative terminal behaves as a north pole while the end connected to the positive terminal behaves as a south pole.
Question - 30 : - When is the force experienced by a current–carrying conductor placed in a magnetic field largest?
Answer - 30 : - When the direction of the current is perpendicular to the direction of the magnetic field is when the force experienced is the largest.