The evaporation of electrons from a heated surface is called
Radiation
Convection
Thermionic emission
Conduction
Correct Answer :
C. Thermionic emission
Related Questions
A positively charged body has
deficit of electrons
excess of neutrons
excess of electrons
deficit of protons
The flux density in an air-cored coil is 10^-3 Wb/m^2. With a cast iron core of relative permeability 100 inserteda the flux density will become
10^-3 Wb/m^2
10^-2 Wb/m^2
10^3 Wb/m^2
0.1 Wb/m^2
The induced emf in a wire loop that is moved parallel to a uniform magnetic field is
Zero
Dependent on the area of the loop
Dependent on the shape of the loop
Dependent on the magnitude of the field
What bond is formed when one or more electrons in the outermost energy orbit of an atom are transferred to another?
Ionic
Covalent
Metallic
Van der Waals
One of the common application of an air- cored choke.
Radio frequency
Audio frequency
Power supply
Power transformer
The ratio between the intensity of magnetization produced in a substance to the magnetizing force producing it
Magnetic Reluctivity
Magnetic Resistivity
Magnetic susceptibility
Magnetic conductivity
How many neutrons does a copper atom have?
The quantity of magnetism retained by a magnetic material after withdrawal of the magnetizing force is called
Leftover magnetism
Hysteresis
Residual magnetism
Coercivity
What is another name for relative permittivity?
Dielectric strength
Electric intensity
Potential gradient
Dielectric constant
Which of the following materials has the least hysteresis loop area?
soft iron
silicon steel
hard steel
wrought iron
A magnetic pole produces 5000 field lines. How much is the flux in webers? A. 50 × 10^-6
5 × 10^-6
500 × 10^-6
500 × 10^-5
The temperature coefficient of resistance of conductors is
positive
zero
negative
infinite
The conduction of electricity across the surface of a dielectric is called
creepage
skin effect
surface effect
crosstalk
The magnetic flux through a coil changes. This results to the induced emf acting in a direction as to
Oppose the change
Aid the change
Either oppose or aid the change
Neither oppose nor aid the change
A one cubic cm of copper has how many free electrons at room temperature?
80 × 10^18
8.5 × 10^22
20 × 10^10
50 × 10^20
A group of magnetically aligned atoms is called
Range
Lattice
Domain
Crystal
The magnetic materials should have a large hysteresis loss for one of the following applications.
Transformers
ACmotors
Permanent Magnets
DC generators
An atom or a group of atoms that carries a net electric charge.
Positive ion
Negative ion
Ion
Electron
Electrons at the outer shell are called
Outer shell electrons
Inner shell electrons
Semiconductor electrons
Valence electrons
The force between two magnetic poles varies with the distance between them. The variation is ______ to the square of that distance.
Equal
Greater than
Directly proportional
Inversely proportional
One oersted (Oe) is equivalent to _____ Gb/cm.
The amount of magnetizing force to counter balance the resid magnetic material is referred to as
Reluctivity
Susceptivity
Coercivity
Retentivity
Why is it that the magnitude of magnetomotive force required for air gap is much greater than that required for iron part of a magnetic circuit?
Because air is a gas
Because air has the highest relative permeability
Because air is a conductor of magnetic flux
Because air has the lowest relative permeability
The force of attraction or repulsion between two magnetic poles is directly proportional to their strengths.
Newton's first law
Faraday's first law of electromagnetic induction
Coulomb's first law
Coulomb's second law
As the magnetic intensity decreasesa the relative permeability of a magnetic material
decreases
remains the same
increases
becomes zero
When the relative permeability of a material is slightly more than 1a it is called ______ material.
diamagnetic
ferromagnetic
paramagnetic
non-magnetic
What is the SI unit of conductivity?
Ohms/m
Ohms-m
Siemens-m
Siemens/m
The net electrical charge in an isolated system remains constant. This is known as
Law of conservation of charge
Coulomb's first law
Coulomb's second law
Law of conservation of energy
This paper does not exhibit electricity because it contains the same number of
protons and electrons
neutrons and electrons
neutrons and positrons
atoms
Small voltages generated by a conductor with current in an external magnetic field.
Skin effect
Magnetic effect
Hall effect
Flywheel Effect