Magnetic Effects Of Electric Current MCQ and Previous Year Questions

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Previous Years Questions

Ques: Describe an activity that illustrates how magnetic field lines are produced when current is passed through a circular coil. (5 marks)

Ans. Aim: To evaluate the magnetic field characteristics produced by a current-carrying circular coil at its center.

Equipment required: Rectangular cardboard with two holes, thick copper circular coils with a known number of turns, key, battery, rheostat, stand, iron filings

Method:

• Pass the coil through the two cardboard holes so that half of the loop is above the cardboard and the other half is below it and normal to the plane of the cardboard.
• Join the circuit.
• Distribute the iron filings evenly on the cardboard.
• Allow current to flow through the coil by inserting the plug into the key.
• Take note of the pattern of iron filings that emerges on the cardboard after a few gentle taps. (Observation).
• Place the compass at any point on the field pattern. Keep an eye on the needle's movement. (Observation No. 2)

Points Observed:

(a) Iron filings are organized in concentric circles.

(b) The concentric circle becomes bigger in size as we walk away from the wire.

(c) Lines are almost straight and perpendicular to the plane of the loop at the loop's center.

To conclude,

• The magnetic field around a current-carrying circular loop is represented by concentric circles at each point.
• The magnetic field line near the loop's axis is straight and perpendicular to the plane of the coil.
• As we move away from the center of the loop, the field lines continue to diverge.

Ques: What exactly is a solenoid? What is the behavior of a current-carrying solenoid? Give its primary function. (3 marks)

Ans Solenoid: A solenoid is a coil of many circular turns of insulated copper wire wound on a cylindrical insulating body (i.e., cardboard, etc.) such that its length exceeds its diameter.

When current flows through the solenoid, the magnetic field line pattern resembles that of a bar magnet with fixed polarity, i.e. North and South poles at its ends, and it acquires the same directive and attractive properties as a bar magnet. The current-carrying solenoid behaves like a bar magnet, as a result.

Use of a current-carrying solenoid: It is used to create both a temporary magnet known as an electromagnet and a permanent magnet.

Ques: What exactly are magnetic field lines? Justify the following claims. (3 marks)

(a) No two magnetic field lines ever intersect.

(b) Magnetic field lines are straight lines.

Ans  Magnetic field lines are defined as the path along which the unit North pole (imaginary) in a magnetic field tends to move if free to do so.

(a) The magnetic lines of force are not intersected (or crossed). If they do, two tangents can be drawn at the point of intersection, indicating that there will be two different directions of the same magnetic field, i.e. the compass needle will point in two different directions, which is not possible.

(b) Magnetic field lines are continuous closed curves. They diverge from a bar magnet's north pole and converge at its south pole. They move from the south pole to the north pole inside the magnet.

Ques: Why and when does a current-carrying conductor in a magnetic field experience force? List the variables that influence the direction of this force. (2 marks)

Ans  The movement of a conductor's free electrons in a specific direction causes current to flow through it. When such a conductor is placed in a uniform magnetic field, each of its drifted electrons experiences a magnetic force. This force is felt collectively by a conductor as a whole. A current-carrying conductor in a magnetic field experiences a force, as a result. The magnetic force direction is determined by I) the direction of current through the conductor and (ii) the direction of the magnetic field.

Ques: How is the strength of the magnetic field near a straight current-conductor?

(i) related to the strength of the current in the conductor?

(ii) is it affected when the direction of current flow in the conductor is changed? (2 marks)

Ans. i)The strength of the magnetic field around a straight current conductor tends to increase with the increase in the conductor’s current strength and vice versa.

(ii)If the direction of current through a straight current-carrying conductor is reversed, the magnetic field direction around that conductor is reversed.

Ques: What basically does the term "frequency of an alternating current" mean? What is its monetary worth in India? Why is alternating current thought to be preferable to direct current for long-distance transmission of electric energy? (3 marks)

Ans 1)The number of cycles completed in one second is equal to the frequency of the alternating current.

2) In India, the frequency of the alternating current is 50 Hz or 50 cycles per second.

3) When compared to direct current, alternating current is considered to be more advantageous for long-distance transmission of electric energy because it can be transmitted over long distances to distant locations with little loss of electric power.

Ques: Describe one significant difference between A.C. and D.C. Why is alternating current preferred over direct current for long-distance electric power transmission? Name one D.C. and one A.C. source each. (2 marks)

Ans The distinction between A.C. and D.C. The alternating current (A.C.) periodically reverses its direction, whereas the direct current (D.C.) always flows in one direction.

A.C. is preferable to D.C. because it can be transmitted over long distances with little energy loss.

Battery as a D.C. source A.C. generator: A.C. source.

Ques: Describe the consequences of a short circuit. Or Short-circuiting is a major cause of fire in office buildings. List three factors that could cause a short circuit. (3 marks)

Ans When a short circuit takes place the current present in the system increases to a great extent while the voltage drops to a great extent. The heavy current present in the system might lead to excessive heating, resulting in giving rise to an explosion or fire. 

Three factors are:

1) The failure of electrical insulation causes the live wire to come into direct contact with the neutral or earth wire.

2) The presence of an external conducting material, such as water, which is accidentally introduced into the circuit.

3) When the moving parts of an electrical appliance become jammed, it is forced to operate.

Ques: Describe any two situations that could result in electrical hazards in domestic circuits. (3 marks)

Ans. The two situations are:

Ques: i) Connecting too many electrical devices to a single socket or an extension cord for an extended period of time draws a high current from the mains, which exceeds the current rating of the connecting wires. The wires cannot withstand such a high current and will melt, potentially causing a fire.

(ii) The majority of electrical hazards in domestic circuits are caused by faulty electrical outlets, as well as old and out-of-date appliances. The chances of a short circuit, or contact of the live and neutral wires with each other, are extremely high due to damage in their insulation or a fault in the appliances. It may cause a spark at the point of contact, which could lead to a fire.

Ques: Identify the current type: (a) found in household supplies. (b) provided by a cell (2 marks)

Ans 

1. A.C. stands for alternating current. 
2. Linear current.

Ques: Give an example of an electromagnetic induction application. (1 mark)

Ans. This phenomenon is used in the production of electricity.

Ques: A compass needle is placed in close proximity to a current-carrying wire. In each of the following cases, state your observation and provide a reason for it. (3 marks)

(a) The electric current in the wire has increased in magnitude.

(b) The compass needle has moved away from the wire.

Ans (a) Observation: The needle's deflection increases.

The magnetic field strength caused by a current-carrying wire increases as the current in the wire increases,

(b) Observation: As the compass needle moves away from the current-carrying wire, its deflection decreases.

Reason: Increase in distance from the wire causes a decrease in the strength of the magnetic field.

Ques: What exactly is short-circuiting? Mention one factor or condition that may contribute to it. Suggest a device in your home that serves as a safety precaution. Describe how it works on a basic level. (5 marks)

Ans Short-circuiting occurs when an electric circuit has very low resistance to the flow of current through it, causing the current to surge and the circuit to be short-circuited. It happens when the live wire comes into contact with the neutral wire. This occurs as a result of damage to the power lines' insulation.

Device for ensuring safety: Fuse.

The fuse's operation is as follows: It is based on the heating effect of an electric current, also known as Joule's law of heating. The heat produced in a resistor, according to this law, is directly proportional to the i) current squared for a given resistance

(ii) resistance for a given current; and (iii) time the current flows through the resistor.

H = I2Rt

As a result, as the current in the circuit increases, the wire with a low melting point melts due to the heat generated. As a result, the circuit breakers and electrical devices, and appliances are protected.

Ques: Which color insulation cover is generally used for earth wire? Why is an earth wire connected to metallic appliance parts? (2 marks)

Ans  Green or yellow insulation is used for earth wire. The earth wire provides a low resistance current path and keeps the potential of the appliance body in unison with that of the earth. As a result, earth wire is used as a safety precaution.

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