Physics M.C.Q (1 Marks)

4. Both A or C.

Explanation:

They are ways of switching using a low current to use an electromagnet to close or open a spring steel contact.They are often used to isolate a user from a high voltage that needs to be switched, using low current, low voltage to operate the relay, rather than having a user come in direct proximity to the higher voltage that needs to be switched.When the current through the electromagnet of a relay reaches a particular value it either breaks the circuit by repllening or closes the circuit by pulling in an iron contact.

3. H = 0

4. Energy.

Explanation:

Lenz's law deals with conversion of mechanical energy into electromagnetic energy in case of electromagnetic induction. Hence Lenz's law is basically a conversion of energy from one form to another.

1. Diamagnetic material only.

3. Tall and wide.

3. 125K

Explanation:

Superconductors are materials that conduct electricity with no resistance. This means that, unlike the more familiar conductors such as copper or steel, a superconductor can carry a current indefinitely without losing any energy.

The upper limit temperature of a superconductor is 125K

2. Ferro-magnetic materials

Explanation:

The substances which are attracted towards a magnet are called ferro-magnetic materials Materials that can be magnetized, which are also the ones that are strongly attracted to a magnet, are called ferromagnetic (or ferrimagnetic). These include iron, nickel, cobalt, some alloys of rare-earth metals, and some naturally occurring minerals such as lodestone.

1. Steel.

3. High retentivity and high coercivity.

Explanation:

Permanent magnets should have high retentivity so that a strong magnetic field persists on removal of magnetic field.

Permanent magnets should have high coercivity so that external magnetic field in opposite direction cannot easily demagnetize the magnet.

3. Tall and wide.

Explanation:

Permanent magnet should have large coercivity and large retentivity. Therefore, the hysteresis cycle of the material should be tall and wide.

1. Not possible.

Explanation:

No. The force on a charge is perpendicular to the direction of the magnetic field at each point.

F = q (v × B).

It is inappropriate to call magnetic field lines as lines of force.

1. 631K

Explanation:

Above 631K Ni behaves like paramagnetic material.

1. Diamagnetism.

Explanation:

Diamagnetism (where orbital motion of electrons creates tiny atomic current loops, which produce magnetic fields) is a property of all materials and opposes applied magnetic fields, but is very weak.

2. Must be diamagnetic.

Explanation:

The permanent magnetic moment of the atoms of a material is zero. The material must be diamagnetic.

1. Energy.

Explanation:

According to Lenz's law an induced electromotive force (emf) always gives rise to a current whose magnetic field opposes the original change in magnetic flux.

It is a common way of understanding how electromagnetic circuits obey newton's third law and the conservation of energy.

1. Space surrounding the magnet in which magnetic force acts.

Explanation:

A magnetic field is generated when electric charge carriers such as electrons move through space or within an electrical conductor. It is the space surrounding the magnet in which magnetic force acts. Its intensity is represented by magnetic lines of force.

2. Coercive force.

Explanation:

The value of H needed to remove the residual magnetism is coercive force or coercivity.

3. Must be ferromagnetic

Explanation:

Unlike paramagnetic materials, the atomic moments in ferromagnetic materials exhibit very strong interactions. These interactions are produced by electronic exchange forces and result in a parallel or antiparallel alignment of atomic moments.

This results in permanent non-zero magnetic moment of atoms in these materials.

3. Induced current flows such that direction of magnetic field produced from induced current opposes change in external magnetic field.

Explanation:

Lenz's Law states that the direction of an induced current is always such as to oppose the change in the circuit or the magnetic field that produces it. So according to this law, induced current flows to oppose the cause.

2. Coercivity.

Explanation:

Coercivity is the magnetic force required to demagnetise the material.

4. All of the above.

3. Paramagnetic materials.

Explanation:

Paramagnetic materials are those when suspended freely inside the magnetic field, it slowly sets itself parallel to the direction of the magnetic field. When placed in a non-uniform magnetic field, it tends to move from weaker to a stronger magnetic field.

4. Both of these.

Explanation:

A moving charge and changing electric field both produces magnetic field.

3. Soft magnetic material

Explanation:

A narrow hysteresis loop implies a small amount of dissipated energy. This occurs as a result of its small area and therefore more frequently repeated reversals of applied magnetising force. Soft magnetic are materials used in devices that require alternating magnetic fields have these narrow hysteresis shapes.

3. Ferromagnetic substances.

Explanation:

Ferromagnetic substance, Because they get magnetize in external magnetic field and don't lose their magnetic property.

3. Electric current

Explanation:

An electric current is produced in the wire. The production of electricity from magnetism is called electromagnetic induction.

1. Magnetic field

Explanation:

A surrounding around a magnet in which source is felt is due to magnetic property of the magnet term as magnetic field.

1. Atomic currents.

2. Above the curie temperature.

Explanation:

Curie - Wiess Law states that all ferromagnetic substances become paramagnteic above the curie temperature.

3. Magnetic intensity and intensity of magnetization are the same.

Explanation:

The statement magnetic intensity and intensity of magnetization are the same is the false one. They are not the same. When a magnet is entering a magnetic field, then the poles of the magnet experiences certain forces. Magnetic intensity refers to the measure of these forces. But, the intensity of magnetization explains the change in the magnetic moment of a magnet as a function of volume. All the other statements are valid.

3. 6.65 s.

2. Artificial magnet.

Explanation:

Artificial magnets are man-made magnets. Magnets that are made from iron in different components shapes and sizes for different uses are called artificial magnets.

2. Magnetic polarization.

Explanation:

Magnetization is also termed as magnetic polarization. Magnetic polarization is basically a balance between the magnetic flux density in a space which is devoid of matter and the magnetic flux density in a space with matter, i.e. in a material.

1. There will be no induced emf in the coil.

Explanation:

Since the coil and the magnet are moving with same velocity, so there will be no change in magnetic flux linked with the coil due to magnet. Hence no emf is induced in the coil.

4. High retentivity, high coercivity and high permeability.

3. Both electric and magnetic fields.

Explanation:

When a charge electron starts to move, electric current generates and this electric current generates magnetic field, a charge at rest also can generate electric field.

1. Vertical plane passing through the axis of a freely suspended or pivoted magnet.

Explanation:

A vertical plane passing through the axis of a freely suspended or pivoted magnet is known as magnetic meridian of Earth. The vertical plane passing through the geographical North Pole and South Pole at a given place is known as the geographical meridian of that place.

1. Repel

Explanation:

Like magnetic force repel each other whereas unlike magnetic poles attract each other.

2. May be zero.
3. May be infinity.
4. May be negative.

Explanation:

When a ferromagnetic material goes through a Hysteresis loop, the Magnetic susceptibility may be zero, may be infinity or may be negative.

3. Continuous.

1. End-on position.

1. Zero

Explanation:

In superconductors, the resistance drops abruptly to zero when the material is cooled below its critical temperature. Thus resistivity of superconductors is zero below its critical temperature.

1. on diverging.

Explanation:

Meena draws a magnetic field lines of field close to the axis of a current carrying circular loop.as she moves away from the centre of the circular loop she observes that the lines keep on diverging.Strength of the magnetic field falls as distance increases. This is indicated by the decrease in degree of closeness of the lines of field.

1. High retentivity and high coercive force.

Explanation:

Permanent magnetis are High retentivity and High coercive force.

1. Iron

Explanation:

Iron is a ferromagnetic substance the property which makes it attach to magnets. This causes the concavity. Chromium is anti-ferromagnetic, wood and carbon are not magnetic materials.

2. Para magnetic material.

Explanation:

Above curie temperature ferromagnetic material behaves like paramganetic materials. There magnetic susceptibilty starts varying linearly with temperature. Their I becomes too small above curies temperature.

Therefore, nature of ferrromagnetic materials becomes paramagnetic.