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All About Electromagnetism – Maharashtra Board Class 10 Solutions for Science and Technology

 All About Electromagnetism – Maharashtra Board Class 10 Solutions for Science and Technology (English Medium)

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Solution 1C:

  1. Bar magnet: With the exception of the bar magnet, all devices work on the principle of electromagnetism.
  2.  Direct current. Direct current is a type of current; the rest are components of an electric motor.
  3.  Generator. The generator is an electric device; the rest are safety measures used in electricity.
  4.  Thermometer. The thermometer is used to measure temperature; the rest are used to measure electrical quantities.

Solution 1B:

  1. True
  2. False. Magnetic field decreases as we go away from a magnet.
  3.  False. Magnetic lines of force never cross each other.
  4.  True

Solution 1A.1:

generator

Solution 1A.2:

increases

Solution 1A.3:

Right-hand rule

Solution 2.1:

A field of force which exists in the space around a magnet or a current-carrying conductor is called a magnetic field.

Solution 2.2:

A coil of many turns of insulated copper wire wrapped in the shape of a cylinder is called a solenoid.

Solution 2.3:

A device which converts electrical energy into mechanical energy is called an electric motor.

Solution 3.1:

Stretch the thumb, forefinger and middle finger of the right hand, so that they are perpendicular to each other. If the forefinger indicates the direction of the magnetic field and the thumb shows the direction of the motion of the conductor, then the middle finger will show the direction of the induced current.

Solution 3.2:

Imagine that you are holding a current-carrying straight conductor in your right hand such that the thumb points towards the direction of current, then the curled fingers around the conductor will give the direction of the magnetic field. This is known as the right-hand thumb rule.

Solution 4:
All About Electromagnetism - Maharashtra Board Class 10 Solutions for Science and Technology-1(4)

Solution 5:

  1. Magnetic lines of force are closed continuous curves. They start from the North Pole and end at the South Pole.
  2. Magnetic lines of force never intersect each other.
  3.  Magnetic lines of force are crowded near the strong magnetic field and are rarer where the field is weak.
  4.  The tangent at any point on a magnetic line of force gives the direction of the magnetic field at that point.

Solution 6.1:

If wires carrying electricity are touched barefooted, a large current may pass our body as our body is a conductor of electricity.
As a result we may get severe shock, which may cause death. Hence, wires carrying electricity should not be touched barefooted.

Solution 6.2:

If many electrical appliances of high power are switched on simultaneously, overloading occurs. Overloading means the flow of a large amount of current in the circuit beyond the permissible value of current. It may cause fire. Hence, we should not use many electrical appliances simultaneously.

Solution 6.3:

Alloys like alnico or nipermag are used to make permanent magnets. Permanent magnets are used in industry, i.e. in a speedometer, microphone, loudspeaker and voltmeter. Hence, alloys like alnico or nipermag are used in industry.

Solution 6.4:

A magnetic crane has an electromagnet. When a current is passed through it, it becomes a temporary magnet. So scrap iron gets attracted to it and sticks to it. Thus, scrap iron can be easily loaded.
After transporting scrap iron to the desired place, the current is stopped. So, the crane loses its magnetism and scrap iron gets separated. Due to this ease in operation, a magnetic crane is used to load and transport scrap iron.

Solution 7.1:

Construction: It has five parts as shown in the figure.
All About Electromagnetism - Maharashtra Board Class 10 Solutions for Science and Technology-2(7.1)
1. Armature coil: It is made of a large number of turns of insulated copper wire wound on an iron core in a rectangular shape.
2. Strong magnet: The armature coil is placed in between the two pole pieces (N and S) of a strong magnet which provides a strong magnetic field.
3. Split-ring commutator: It is a metallic ring having two halves, R1and R2,to which the ends of the armature coil are connected. The commutator reverses the direction of the current in the armature coil.
4. Brushes: Two brushes B1 and B2 are used to press the commutator.
5. Battery: The battery supplies the current to the armature coil.
Working: When current is passed through the coil ABCD, arms AB and CD experience force. Arm AB experiences a force in the upward direction, while arm CD experiences a force in the downward direction according to Fleming’s left-hand rule. These forces are equal and opposite. These forces rotate the coil in the clockwise direction until the coil is vertical. At this position, the contact between the commuter and brushes break. So, the supply to the coil is cut off. Hence, no force acts on the coil. But the coil does not stop due to inertia. It goes on rotating until the commutator comes in contact with the brushes.
Again, the current flows through the coil, and arm AB rotates through 90°, 180°, 270° and 360°. Now, the force acting on arm AB is downward and that on arm CD is upward. Again this force moves the coil in the clockwise direction. Thus, the rotational motion of the coil is continued.
The coil of the DC motor continues to rotate in the same direction.

Solution 7.2:

Electrical generators are of two types – AC and DC generators
Electric AC generator
 Construction: It has four parts as shown in the figure.
All About Electromagnetism - Maharashtra Board Class 10 Solutions for Science and Technology-3(7.2)

1. Armature coil: Coil ABCD consists of a large number of turns of insulated copper wire wound on an iron core in rectangular shape.
2. Strong magnet: The armature coil is placed in between the two pole pieces (N and S) of a strong magnet which produces a strong magnetic field.
3. Slip rings: The two ends of the armature coil are connected to the brass rings R1 and R2 which rotate along with the coil.
4. Brushes: Two carbon brushes B1 and B2 in contact with the rings R1 and R2 are used to carry the current to the external circuit. The galvanometer (G) shows the direction of the current in the external circuit.
Working: When the armature coil ABCD rotates in the magnetic field, it cuts the magnetic lines of force. The changing magnetic field produces induced current in the coil. The direction of the induced current is determined by Fleming’s right-hand rule. In the first-half rotation of the coil, the current flows out through the brush B1 in one direction. In the next half rotation of the coil, the current flows out through the brush B2 in the reverse direction. This process is repeated; hence, the induced current produced is of alternating nature. So, it is called alternating current.

Electric DC generator:
All About Electromagnetism - Maharashtra Board Class 10 Solutions for Science and Technology-4(7.2)
Construction: It has five parts as shown in the figure.
1. Armature coil: Coil ABCD consists of a large number of turns of insulated copper wire wound on an iron core in the rectangular shape.
2. Strong magnet: The armature coil is placed in between the two pole pieces (N and S) of a strong magnet which produces a strong magnetic field.
3. Slip rings: The two ends of the armature coil are connected to the brass rings R1 and R2 which rotate along with the coil.
4. Brushes: Two carbon brushes B1 and B2 are used to press the commutator.
5. Bulb: The electric bulb is connected across the brushes and shows the output of the generator. The bulb glows when there is a current in the circuit.
Working: When the coil of a DC generator rotates in the magnetic field, a potential difference is produced in the coil. So, the current flows which is shown by glowing of the bulb.
In a DC generator, one brush is always in contact with the arm of the armature moving up, while the other brush is in contact with the arm of the coil moving down in the magnetic field. Hence, the flow of current in the circuit is in the same direction as long as the coil rotates in the magnetic field.