01) Indicate ___________ material does not retain magnetism permanently..
Answer: Soft iron
02) The ratio of intensity of magnetization to the magnetization force is known as_________.
Answer: Susceptibility
03) ___________ is not a unit of flux?
Answer: Tesla
04) If a copper disc is rotated rapidly below a freely suspended magnetic needle, the magnetic needle shall start rotating with a velocity ____________.
Answer: Less than that of disc and in the same direction
05) A permeable substance is one __________.
Answer: Through which the magnetic lines of force can pass very easily
06) A certain amount of current flows through a ring-shaped coil with fixed number of turns. How does the magnetic induction B varies inside the coil if an iron core is threaded into coil without dimensional changes of coil?
Answer: Increases
07) Temporary magnets are used in_________.
Answer: Loudspeakers, Generators, Motors
08) Ampere-turn is the unit of magneto-motive force (mmf). True/false.
Answer: True
09) __________ is expected to have the maximum permeability?
Answer: Ebonite
10) The magnetic reluctance of a material ______________.
Answer: Decreases with increasing cross sectional area of material
11) The direction of a magnetic field within a magnet is __________.
Answer: From south to north
12) A 300 mm long conductor is carrying a current of 10 A and is situated at right angles to a magnetic field having a flux density of 0.8 T; The force on the conductor will be _____________.
Answer: 2.4 N
13) Electromagnetic induction is the force that produces a magnetic field. True/false.
Answer: False
14) A square cross-sectional magnet has a pole strength of 1 × 10 Wb and cross sectional area of 20 mm × 20 mm. What is the strength at a distance of 100 mm from the unit pole in air?
Answer: `\frac{6338 N}{Wb}`
15) The commonly used material for shielding or screening magnetism is ___________.
Answer: Soft iron
16) The unit for reluctance is ___________.
Answer: At/Wb
17) Hysteresis loop in case of magnetically hard materials is more in shape __________ as compared to magnetically soft materials.
Answer: Rectangular
18) An electromagnetic field exists only when there is _____________.
Answer: Current
19) What will be the current passing through the ring shaped air cored coil when _________ number of turns is 800 and ampere turns are 3200?
Answer: 4
20) The susceptibility of paramagnetic materials generally lies between ___________.
Answer: `KT_3` and `1^{CT6}`
21) Main causes of noisy solenoid are ____________.
Answer: Strong tendency of fan out of laminations at the end caused by repulsion among magnetic lines of force, Uneven bearing surface, caused by dirt or uneven wear between moving and stationary parts
22) A basic one-loop dc generator is rotated at 90 rev/s. How many times each second does the dc output voltage peak (reach maximum)?
Answer: 180
23) Paramagnetic materials have relative permeability _________.
Answer: Slightly more than unity
24) When the speed at which a conductor is moved through a magnetic field is increased, the induced voltage ____________.
Answer: Increases
25) A relay is an electromagnetically controlled mechanical device in which electrical contacts are opened or closed by a magnetizing current. True/false.
Answer: True
26) The magnetism left in the iron after exciting field has been removed is known as _________.
Answer: Residual magnetism
27) When the north poles of two bar magnets are brought close together, there will be ________.
Answer: A force of repulsion
28) Susceptibility is positive for ___________.
Answer: Ferromagnetic substances
29) If a loop in a basic dc generator suddenly begins rotating at a faster speed, the induced voltage __________.
Answer: Increases
30) The most effective and quickest may of making a magnet from soft iron is by ___________.
Answer: Placing it inside a coil carrying current
31) When the current through the coil of an electromagnet reverses, the _________.
Answer: Direction of the magnetic field reverses
32) A keeper is used to _________.
Answer: Provide a closed path for flux
33) The unit for permeability is _________.
Answer: Wb/At × m
34) What will be the magnetic potential difference across the air gap of 2 cm length in magnetic field of 200 AT/m?
Answer: 4 AT
35) When a solenoid is activated, the force that moves the plunger is _________.
Answer: An electromagnetic field
36) How does the magnetic compass needle behave in a magnetic field?
Answer: It assures a position which follows a line of magnetic flux
37) If a conductor is moved back and forth at a constant rate in a constant magnetic field, the voltage in the conductor will reverse polarity. True/false.
Answer: True
38) For which of the following materials the saturation value is the highest?
Answer: Ferrites
39) There is 900 mA of current through a wire with 40 turns. What is the reluctance of the circuit if the flux is 400 μWb? .
Answer: 90,000 At/Wb
40) Magnetism of a magnet can be destroyed by ___________.
Answer: Heating, Hammering, By inductive action of another magnet
41) The voltage induced across a certain coil is 200 mV. A 120 Ω resistor is connected to the coil terminals. The induced current is ________.
Answer: 1.7 mA
42) Ferrites are materials...
Answer: Ferromagnetic
43) A material which is slightly repelled by a magnetic field is known as _____.
Answer: Diamagnetic material
44) What is the flux density when the flux is 5.5 μWb and the cross-sectional area is 6 × `10^{–3}` `m^2`?
Answer: 917 μT
45) Materials subjected to rapid reversal of magnetism should have ___________.
Answer: High permeability and low hysteresis loss
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