Magnetic Effects of Electric CurrentClass 10 Physics NCERT Solutions
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Q1E X E R C J S E S
Which of the following correctly describes the magnetic field near a long straight wire?
(a)
The field consists of straight lines perpendicular to the wire.
(b)
The field consists of straight lines parallel to the wire.
(c)
The field consists of radial lines originating from the wire.
(d)
The field consists of concentric circles centred on the wire.
Solution
The correct option is (d) The field consists of concentric circles centred on the wire.
Explanation:
As described in Section 12.2.1 and demonstrated in Activity 12.5, when an electric current passes through a long straight conductor, it generates a magnetic field around it. The magnetic field lines are in the form of concentric circles with the wire at their center. The plane of these circles is perpendicular to the length of the wire. The direction of the magnetic field at any point on these circles is given by the Right-Hand Thumb Rule.
Q2E X E R C J S E S
At the time of short circuit, the current in the circuit
(a)
reduces substantially.
(b)
does not change.
(c)
increases heavily.
(d)
vary continuously.
Solution
The correct option is (c) increases heavily.
Explanation:
A short circuit occurs when the live wire and the neutral wire come into direct contact, often due to damaged insulation. This creates a path of very low resistance for the current to flow. According to Ohm's law (), when the resistance () decreases drastically while the potential difference () remains the same, the current () in the circuit increases abruptly and heavily. This large current can cause overheating and damage the circuit and appliances.
Q3E X E R C J S E S
State whether the following statements are true or false.
(a)
The field at the centre of a long circular coil carrying current will be parallel straight lines.
(b)
A wire with a green insulation is usually the live wire of an electric supply.
Solution
(a) True. A long circular coil carrying current is a solenoid. As stated in Section 12.2.4, the magnetic field lines inside a current-carrying solenoid are in the form of parallel straight lines. This indicates that the magnetic field is uniform and strong inside the solenoid.
(b) False. In domestic electric circuits, the wire with green insulation is the earth wire. The live wire usually has red insulation, and the neutral wire has black insulation. The earth wire is a safety measure to protect users from electric shock in case of current leakage to the metallic body of an appliance.
Q4E X E R C J S E S
List two methods of producing magnetic fields.
Solution
Based on the chapter, two methods of producing magnetic fields are:
-
Using a Permanent Magnet: A permanent magnet, such as a bar magnet, has a natural magnetic field in the region surrounding it. This field can be detected by the force it exerts on other magnetic materials or a compass needle.
-
Using Electric Current: An electric current flowing through a conductor produces a magnetic field around it. This phenomenon is known as the magnetic effect of electric current, first observed by Hans Christian Oersted. The shape of the magnetic field depends on the shape of the conductor (e.g., straight wire, circular loop, or solenoid).
Q5E X E R C J S E S
When is the force experienced by a current-carrying conductor placed in a magnetic field largest?
Solution
The force experienced by a current-carrying conductor placed in a magnetic field is largest when the direction of the electric current is perpendicular (at a right angle, or ) to the direction of the magnetic field. As mentioned in Section 12.3, experiments show that the displacement of the conductor, which is a measure of the force, is highest under this condition.
Q6E X E R C J S E S
Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of magnetic field?
Solution
To determine the direction of the magnetic field, we can use Fleming's Left-Hand Rule. First, we need to identify the directions of the current and the force.
-
Direction of Current: The electron beam moves from the back wall to the front wall. By convention, the direction of electric current is taken as opposite to the direction of motion of electrons. Therefore, the direction of the current is from the front wall towards the back wall.
-
Direction of Force: The electron beam is deflected to your right side. This is the direction of the magnetic force acting on the beam.
-
Applying Fleming's Left-Hand Rule:
- Stretch the thumb, forefinger, and middle finger of your left hand so they are mutually perpendicular.
- Point the middle finger in the direction of the current (from front to back).
- Point the thumb in the direction of the force (to your right).
- The forefinger will now point in the direction of the magnetic field.
Following this, your forefinger will point in the vertically downward direction.
Final Answer: The direction of the magnetic field is vertically downwards.
Q7E X E R C J S E S
State the rule to determine the direction of a (i) magnetic field produced around a straight conductor-carrying current, (ii) force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it, and (iii) current induced in a coil due to its rotation in a magnetic field.
Solution
(i)
Magnetic field produced around a straight conductor-carrying current:
The direction of the magnetic field is determined by the Right-Hand Thumb Rule. According to this rule, if you imagine holding the current-carrying straight conductor in your right hand such that the thumb points in the direction of the current, then the direction in which your fingers wrap around the conductor gives the direction of the magnetic field lines.
(ii)
Force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it:
The direction of the force is determined by Fleming's Left-Hand Rule. According to this rule, if you stretch the thumb, forefinger, and middle finger of your left hand so that they are mutually perpendicular, and if the forefinger points in the direction of the magnetic field and the middle finger points in the direction of the current, then the thumb will point in the direction of the force or motion of the conductor.
(iii)
Current induced in a coil due to its rotation in a magnetic field:
The direction of the induced current is determined by Fleming's Right-Hand Rule. (Note: This rule is not described in the provided source text, which primarily covers the magnetic effect of current and the force on a conductor. The principle of electromagnetic induction and Fleming's Right-Hand Rule are typically discussed in the subsequent sections of the chapter.)
Q8E X E R C J S E S
When does an electric short circuit occur?
Solution
An electric short circuit occurs when the live wire and the neutral wire in an electric circuit come into direct contact with each other. This can happen due to factors like:
- The insulation of the wires getting damaged or wearing out over time.
- A fault or defect within an electrical appliance.
When the live and neutral wires touch, the resistance of the circuit becomes extremely low. This causes a very large amount of current to flow through the circuit abruptly. This phenomenon of a sudden, heavy flow of current is called short-circuiting and can lead to overheating, fire, and damage to the electrical circuit and appliances.
Q9E X E R C J S E S
What is the function of an earth wire? Why is it necessary to earth metallic appliances?
Solution
Function of an earth wire:
The primary function of an earth wire is to act as a safety measure, protecting users from severe electric shocks. It provides a low-resistance path for any leakage current to flow directly into the earth.
Necessity of earthing metallic appliances:
It is necessary to earth appliances with metallic bodies (like electric irons, refrigerators, toasters, etc.) for safety. If, due to some fault, the live wire touches the metallic casing of the appliance, the current can flow through the casing. Without an earth wire, anyone touching the appliance would get a severe electric shock as the current would pass through their body to the ground.
When the appliance is earthed, the metallic body is connected to the earth wire. In case of a current leakage to the body, the earth wire provides an easy, low-resistance path for the current to flow to the earth. This causes a large current to flow, which in turn blows the fuse and disconnects the appliance from the power supply, thus preventing any electric shock to the user.