Magnetism and Magnetic effect of electric current Online Test 12th Science Questions

Historically the word ‘magnetism’ was derived from which ore?

In 1820, Who observed the deflection of magnetic compass needle kept near a current carrying wire?

Magnetic sensing in eyes – for Zebra finch bird, due to which protein present in retina?

Who in 1600 proposed that Earth itself behaves like a gigantic powerful bar magnet?

The branch of physics which deals with the Earth’s magnetic field is called ____

Which among the following quantity is not required to specify the magnetic field of the earth on its surface?

Day and night occur because Earth spins about an axis called ____

A vertical plane passing through the geographic axis is called _____

Which among the following statement is correct
1) The straight line which connects magnetic poles of Earth is known as needle axis. A vertical plane passing through needle axis is called magnetic meridian and a great circle perpendicular to Earth’s needle axis is called magnetic equator.
2) When a magnetic needle is freely suspended, the alignment of the magnet does not exactly lie along the geographic meridian.

The angle between magnetic meridian at a point and geographical meridian is called _____

The angle subtended by the Earth’s total magnetic field  B with the horizontal direction in the magnetic meridian is called _____

The horizontal component of Earth’s magnetic field, denoted by ____

1. B_T
2. B_M
3. B_C
4. B_H

Which among the following statement is correct

1. Let B_E be the net Earth’s magnetic field at any point on the surface of the Earth. B_E can be resolved into two perpendicular components. Horizontal component B_H = B_E cos I. Vertical component B_V = B_E sin I. By dividing both vertical and horizontal, tan I = BV/BE.
2. At magnetic equator, Earth’s magnetic field is parallel to the surface of the Earth (i.e., horizontal) which implies that the needle of magnetic compass rests horizontally at an angle of dip, I = 180^o., B_H = B_E., B_V = 0. This implies that the horizontal component is minimum and vertical component is maximum at the equator.
3. At magnetic poles, Earth’s magnetic field is perpendicular to the surface of the Earth (i.e., vertical) which implies that the needle of magnetic compass rests vertically at an angle of dip, I = 90^o. Hence, B_H = 0., B_V = B_E. This implies that the vertical component is maximum at poles and horizontal component is zero at poles.

The horizontal component and vertical component of Earth’s magnetic field at a place are 0.15 G and 0.26 G respectively. Calculate the angle of dip and resultant magnetic field. (G-gauss, cgs unit for magnetic field 1G = 10–4 T)?

Which is defined as the product of its pole strength and magnetic length?

Which among the following statement is correct

1. Consider a bar magnet. Let q_m be the pole strength of the magnetic pole and let l be the distance between the geometrical centre of bar magnet O and one end of the pole. The magnetic dipole moment is defined as the product of its pole strength and magnetic length. It is a vector quantity, denoted by p_m.
2. P_m = q_m + d. where d is the vector drawn from north pole to south pole and its magnitude r |d| = 2l. The SI unit of magnetic moment is Am³. The direction of magnetic moment is from south pole to north pole.

What was the other name of northern lights?

Northern lights and Southern lights are often called as _____

Which among the following statement is incorrect

1. Polar lights are called as “Aurora borealis” in the north and “Aurora australis” in the south. This occurs as a result of interaction between the gaseous particles in the Earth’s atmosphere with highly charged particles released from the Sun’s atmosphere through solar wind.
2. These particles emit light due to collision and variations in colour are due to the type of the gas particles that take part in the collisions. A pale yellowish – green colour is produced when the ionized carbon takes part in the collision and a blue or purplish – red aurora is produced due to ionized hydrogen molecules.

Which is defined as a force experienced by the bar magnet of unit pole strength?

What is the unit of magnetic field?

1. N A m
2. N A^-1 m^-1
3. N A^-1 m^-2
4. N A^-2 m^-2

If the magnet is in the form of rectangular shape or cylindrical shape, then it is known ___

Which among the following is the natural magnet?

Which among the following statement is correct regarding properties of magnet
1) A freely suspended bar magnet will always point along the east-west direction. A magnet attracts or repels another magnet or magnetic substances towards itself. The attractive or repulsive force is maximum near the end of the bar magnet. When a bar magnet is dipped into iron filling, they repel to the ends of the magnet.
2) When a magnet is broken into pieces, each piece behaves like a magnet with poles at its ends. Two poles of a magnet have pole strength equal to one another.
3) The length of the bar magnet is called geometrical length and the length between two magnetic poles in a bar magnet is called magnetic length. Magnetic length is always slightly smaller than geometrical length. The ratio of magnetic length and geometrical length is 5 / 6.

Compute the magnetic length of a uniform bar magnet if the geometrical length of the magnet is 12 cm.

Which among the following statement is correct regarding magnetic lines
1) Magnetic field lines are continuous closed curves. The direction of magnetic field lines is from North pole to South pole outside the magnet and from South pole to North pole inside the magnet.
2) The direction of magnetic field at any point on the curve is known by drawing tangent to the magnetic field lines at that point. Magnetic field lines never intersect each other. Otherwise, the magnetic compass needle would point towards two different directions, which is not possible.
3) The degree of closeness of the field lines determines the relative strength of the magnetic field. The magnetic field is weak where magnetic field lines crowd and strong where magnetic field lines are well separated.

The number of magnetic field lines crossing any area normally is defined as ______

The SI unit for magnetic flux is _____

The CGS unit of magnetic flux is _____

Which is defined as the number of magnetic field lines crossing per unit area kept normal to the direction of lines of force?

What is the unit of Magnetic flux density?

Which among the following statement is correct
1) Magnetic field is said to be uniform if it has same magnitude and direction at all the points in a given region. Example, locally Earth’s magnetic field is uniform. The magnetic field of Earth has same value over the entire area of your school!
2) Magnetic field is said to be non-uniform if the magnitude or direction or both vary at different points in a region. Example: magnetic field of a bar magnet.

Which among the following statement is correct regarding coulomb’s inverse square law of magnetism.
Consider two bar magnets A and B. When the north pole of magnet A and the north pole of magnet B or the south pole of magnet A and the south pole of magnet B are brought closer, they repel each other. On the other hand, when the north pole of magnet A and the south pole of magnet B or the south pole of magnet A and the north pole of magnet B are brought closer, their poles attract each other.
This looks similar to Coulomb’s law for static charges studied (opposite charges attract and like charges repel each other). So analogous to Coulomb’s law in electrostatics, we can state Coulomb’s law for magnetism.
The force of attraction or repulsion between two magnetic poles is directly proportional to the product of their pole strengths and inversely proportional to the square of the distance between them. Mathematically, we can write in magnitude F = k (qmA BmB)/r2.

The repulsive force between two magnetic poles in air is 9 × 10^–3 N. If the two poles are equal in strength and are separated by a distance of 10 cm, calculate the pole strength of each pole?

1. 10 NT^-1
2. 20 NT^-1
3. 30 NT^-1
4. 40 NT^-1

Which is defined as the ability of the materials to retain the magnetism in them even after the magnetising field disappears?

Which among the following statement is correct regarding hysteresis?

1. When a ferromagnetic material is kept in a magnetising field, the material gets magnetised by induction. An important characteristic of ferromagnetic material is that the variation of magnetic induction B with magnetising field H is not linear. It means that the ratio B / H = µ is not a constant.
2. A ferromagnetic material (example, Iron) is magnetised rapidly by a magnetising field H. The magnetic induction B of the material increases from point A with the magnitude of the magnetising field and then attains a critical level. This response of the material is depicted by the path AC. Critical magnetization is defined as the maximum point up to which the material can be magnetised by applying the magnetising field.
3. If the magnetising field is now reduced, the magnetic induction also decreases but does not retrace the original path CA. It takes different path CD. When the magnetising field is zero, the magnetic induction is not zero and it has positive value. This implies that some magnetism is left in the specimen even when H = 0. The residual magnetism AD present in the specimen is called remanence or retentivity.

The magnitude of the reverse magnetising field for which the residual magnetism of the material vanishes is called _____

The phenomenon of lagging of magnetic induction behind the magnetising field is called ___

Which among the following statement is incorrect

1. During the magnetisation of the specimen through a cycle, there is loss of energy in the form of heat. This loss is attributed to the rotation and orientation of molecular magnets in various directions. It is found that the energy lost (or dissipated) per unit volume of the material when it is carried through one cycle of magnetisation is equal to the area of the hysteresis loop.
2. Based on the shape and size of the hysteresis loop, ferromagnetic materials are classified as soft magnetic materials with smaller area and hard magnetic materials with larger area. In Soft ferromagnetic materials area of the loop is small, low retentivity, less hysteresis loss. In Hard ferromagnetic materials area of loop is large, high retentivity and more hysteresis loss.

Which among the following is not the Soft ferromagnetic material?

Which among the following information is not given by hysteresis loop?

The materials with high retentivity, high coercivity and low permeability are suitable for making which magnet?

Which among the following is not the example of electromagnets?

Which among the following is the core of the transformer?

Which among the following statement is correct regarding Oersted experiment

1. In 1820 Hans Christian Oersted, while preparing for his lecture in physics, noticed that electric current passing through a wire deflects the nearby magnetic needle in the compass. By proper investigation, he observed that the deflection of magnetic needle is due to the change in magnetic field produced around current carrying conductor.
2. When the direction of current is reversed, the magnetic needle is deflected in the opposite direction. This lead to the development of the theory ‘electromagnetism’ which unifies two branches in physics namely, electricity and magnetism.

Which among the following statement is correct regarding Current carrying straight conductor?

1. Suppose we keep a magnetic compass near a current-carrying straight conductor, then the needle of the magnetic compass experiences a torque and deflects to align in the direction of the magnetic field at that point.
2. Tracing out the direction shown by magnetic needle, we can draw the magnetic field lines at a distance. For a straight current-carrying conductor, the nature of magnetic field is like concentric circles having their common centre on the axis of the conductor.
3. The direction of circular magnetic field lines will be always clockwise independent on the direction of current in the conductor. If the strength (or magnitude) of the current is increased then the density of the magnetic field will decrease. The strength of the magnetic field (B) decreases as the distance (r) from the conductor also decreases.

Which among the following is not the example of permanent magnets?

Which among the following statement is correct regarding Circular coil carrying current?
1) Suppose we keep a magnetic compass near a current carrying circular conductor, then the needle of the magnetic compass experiences a torque and deflects to align in the direction of the magnetic field at that point.
2) We can notice that at the points A and B in the vicinity of the coil, the magnetic field lines are circular. The magnetic field lines are nearly perpendicular to other near the centre of the loop, indicating that the field present near the centre of the coil is almost non-uniform.
3) The strength of the magnetic field is increased if either the current in the coil or the number of turns or both are increased. The polarity (north pole or south pole) depends on the direction of current in the loop.

Assume that we hold the current carrying conductor in our right hand such that the thumb points in the direction of current flow, then the fingers encircling the conductor point in the direction of ______

Whose right hand cork screw rule can also be used to find the direction of the magnetic field around the current-carrying conductor?

Soon after Oersted’s discovery, who in 1819 did quantitative experiments on the force experienced by a magnet kept near current carrying wire and arrived at a mathematical expression that gives the magnetic field?

Which among the following is incorrect: Biot and Savart experimentally observed that the magnitude of magnetic field dB at a point P at a distance r from the small elemental length taken on a conductor carrying current varies

What is the value of K in SI units in dB = K (I dl)/r^2 sinθ.?

Which among the following statement is correct
1) Electric current is not a scalar quantity. It is a vector quantity. But electric current in a conductor has direction of flow. Therefore, the electric current flowing in a small elemental conductor can be taken as scalar quantity i.e. Idl.
2) Electric and magnetic fields both obey inverse square law, so they are long range fields and obey the principle of superposition and are linear with respect to source. In magnitude, E α q. B α Idl.

Which among the following statement is incorrect regarding electric field?

Which among the following statement is incorrect regarding magnetic field?

Which is a device used to detect very small currents?

Which among the following statement is correct regarding tangent law
1) When a magnetic needle or magnet is freely suspended in two mutually perpendicular uniform magnetic fields, it will come to motion in the direction of the resultant of the two fields.
2) Let B be the magnetic field produced by passing current through the coil of the tangent galvanometer and BH be the horizontal component of Earth’s magnetic field. Under the action of two magnetic fields, the needle comes to rest making angle θ with BH, such that B = BH tan θ.

Which among the following statement is correct regarding Tangent Galvanometer?
1) Tangent Galvanometer (TG) consists of iron coil of several turns wound on a non-magnetic circular frame. The frame is made up of nickel or mica which is mounted vertically on a horizontal base table (turn table) with four levelling screws. The TG is provided with two or more coils of different number of turns.
2) Most of the equipment’s we use in laboratory, contains coils of 2 turns, 5 turns and 50 turns which are of different thickness and are used for measuring currents of different strengths. At the centre of turn table, there is a small upright projection on which a compass box is placed. Compass box consists of a small magnetic needle which is pivoted at its centre, such that the centres of both magnetic needle and circular coil exactly coincide.
3) A thin aluminium pointer attached perpendicular to the magnetic needle moves over a graduated circular scale. The circular scale is divided into four quadrants and they are graduated in degrees, each quadrant being numbered from 0° to 90° In order to avoid parallax error in measurement, a mirror is placed below the aluminium pointer.

Which among the following statement is correct regarding precautions of Tangent galvanometer
1) All the nearby magnets and magnetic materials are kept away from the instrument. Using spirit level, the levelling screws at the base are adjusted so that the small magnetic needle is exactly horizontal and also coil (mounted on the frame) is exactly vertical.
2) The plane of the coil is kept parallel to the small magnetic needle by rotating the coil about its vertical axis. So that, the coil remains in magnetic meridian. The compass box alone is rotated such that the aluminium pointer reads 0o – 0o.

Which among the following statement is correct
In the tangent galvanometer experiment, when no current is passed through the coil, the small magnetic needle lies along horizontal component of Earth’s magnetic field. When the circuit is closed, the electric current will pass through the circular coil and produce magnetic field at the centre of the coil.
Now there are two fields which are acting mutually perpendicular to each other. They are: (1) the magnetic field (B) due to the electric current in the coil acting normal to the plane of the coil. (2) the horizontal component of Earth’s magnetic field (BH)
Because of these crossed fields, the pivoted magnetic needle deflects through an angle θ. From tangent law, B = BH tan θ. When an electric current is passed through a circular coil of radius R having N turns, the magnitude of magnetic field at the centre is B = ¬ µ0NI/2R. By equating both equation, The horizontal component of Earth’s magnetic field is given by BH = (µN)/2R I/tan⁡q .

A coil of a tangent galvanometer of diameter 0.24 m has 100 turns. If the horizontal component of Earth’s magnetic field is 25 × 10–6 T then, calculate the current which gives a deflection of 60o?

If we curl the fingers of right hand in the direction of current in the loop, then the stretched thumb gives which direction in Right hand thumb rule?

Which law is used to calculate magnetic field at a point whenever there is a symmetry in the problem?

Ampère’s law: The line integral of magnetic field over a closed loop is what times net current enclosed by the loop?

Compute the magnitude of the magnetic field of a long, straight wire carrying a current of 1 A at distance of 1m from it. Compare it with Earth’s magnetic field?

Which is a long coil of wire closely wound in the form of helix and When electric current is passed through the solenoid, the magnetic field is produced?

The direction of magnetic field due to solenoid is given by which rule?

Inside the solenoid, the magnetic field is nearly uniform and parallel to its axis whereas, outside the solenoid the field is negligibly ____

The current carrying solenoid is held in right hand. If the fingers curl in the direction of current, then extended thumb gives the direction of ___

Which among the following statement is correct

What is the unit of magnetic flux?

1. T m
2. T m²
3. T m^-2
4. T m^-1

A circular antenna of area 3 m² is installed at a place in Madurai. The plane of the area of antenna is inclined at 47^o with the direction of Earth’s magnetic field. If the magnitude of Earth’s field at that place is 4.1 × 10^–5 T find the magnetic flux linked with the antenna?

Which among the following statement is correct regarding first Faraday’s Experiments on Electromagnetic Induction?

1. Consider a closed circuit consisting of a coil C of insulated wire and a galvanometer G. The galvanometer does not indicate deflection as there is no electric current in the circuit. When a bar magnet is inserted into the stationary coil, with its north pole facing the coil, there is a momentary deflection in the galvanometer.
2. This indicates that an electric current is set up in the coil. If the magnet is kept stationary inside the coil, the galvanometer does not indicate deflection. The bar magnet is now withdrawn from the coil, the galvanometer again gives a momentary deflection but in the opposite direction. So, the electric current flows in opposite direction. Now if the magnet is moved faster, it gives a larger deflection due to a greater current in the circuit
3. The bar magnet is reversed i.e., the south pole now opposes the coil. When the above experiment is repeated, the deflections are opposite to that obtained in the case of north pole. It is concluded that whenever there is a relative motion between the coil and the magnet, there is no deflection in the galvanometer, indicating the electric current setup in the coil.

A circular loop of area 5 × 10^–2 m² rotates in a uniform magnetic field of 0.2T. If the loop rotates about its diameter which is perpendicular to the magnetic field as shown in figure. Find the magnetic flux linked with the loop when its plane is (i) normal to the field (ii) inclined 60^o to the field and (iii) parallel to the field.

1. (i) Φ_B = 2 × 10^-2 Wb; (ii) Φ_B = 8.66 × 10^-3 Wb; (iii) Φ_B = 1 × 10^-2 Wb
2. (i) Φ_B = 0; (ii) Φ_B = 1.66 × 10^-3 Wb; (iii) Φ_B = 1 × 10^-2 Wb
3. (i) Φ_B = 1 × 10^-2 Wb; (ii) Φ_B = 8.66 × 10^-3 Wb; (iii) Φ_B = 0
4. (i) Φ_B = 2 × 10^-2 Wb; (ii) Φ_B = 1.66 × 10^-3 Wb; (iii) Φ_B = 0

Which among the following statement is correct regarding Second Experiment of Faraday’s Experiments on Electromagnetic Induction?

1. Consider two closed circuits. The circuit consisting of a coil P, a battery B and a key K is called as primary circuit while the circuit with a coil S and a galvanometer G is known as secondary circuit. The coils P and S are kept at rest in close proximity with respect to one another. If the primary circuit is closed, electric current starts flowing in the primary circuit.
2. At that time, the galvanometer gives a momentary deflection. After that, when the electric current reaches a certain steady value, no deflection is observed in the galvanometer. Likewise, if the primary circuit is broken, the electric current starts decreasing and there is again a sudden deflection but in the opposite direction.
3. When the electric current becomes zero, the galvanometer shows no deflection. From the above observations, it is concluded that whenever the electric current in the primary circuit changes, the galvanometer shows a deflection.