1. Since every iron atom is a tiny magnet, why aren\'t all iron materials themse
ID: 1451774 • Letter: 1
Question
1. Since every iron atom is a tiny magnet, why aren't all iron materials themselves magnets?
A) They need current to be initially magnetized.
B) The atoms are too far below the surface to have any effect.
C) The groups of atoms point in random directions and the fields cancel out.
D) Only a certain kind of iron can be magnetized.
E) None of the above.
2. An electron always experiences a force in an electric field, but it does not always experience a force in a magnetic field. When doesn't a moving charged particle experience a force in a magnetic field?
A) when the charge is near the magnet's south pole
B) when the charge moves in the same direction as or opposite to the magnetic field
C) when the charge moves perpendicularly to the magnetic field
D) when the charge moves in a path other than a straight line.
E) None of the above
3. The magnetic field around a current-carrying wire is proportional to ________ and inversely proportional to ____________.
A) the distance from the wire, the electron drift speed
B) the electron drift speed, the distance from the wire
C) the current, the distance from the wire
D) the current, the length of the wire,
E) None of the above
4. Two parallel current-carrying wires will _______ if their currents are in the same direction, and will _______ if their currents are in opposite directions.
A) repel, repel
B) attract, attract
C) attract, repel
D) repel, attract
E) None of the above
5. An electric motor
A) Changes electric energy into mechanical energy.
B) Changes mechanical energy into electrical energy.
C) Changes heat into mechanical energy.
D) Changes mechanical energy into heat.
E) None of the above.
6. An electric generator
A) Changes electric energy into mechanical energy.
B) Changes mechanical energy into electrical energy.
C) Changes heat into mechanical energy.
D) Changes mechanical energy into heat.
E) None of the above.
7. Why does an iron core increase the magnetic induction of a coil wire?
A) The iron causes the coil to become magnetized.
B) The iron makes it easier for current to flow in the wire.
C) The magnetic domains in the iron line up with the magnetic field produced inside the coil.
D) The iron acts as a magnetism 'sink' to prevent the build-up of excess magnetism in the coils.
E) None of the above.
8. Why does a transformer require alternating current?
A) Direct current would be too strong for the transformer.
B) The current must reach resonance in order for the transformer to work.
C) Direct currents are only used to transmit electric power over long distance.
D) A changing current produces a changing magnetic field which can produce a current.
E) None of the above
9. Some of the reasons AC is used instead of DC to power cities are that
I) AC-production is more environmentally friendly than dc-production.
II) AC can be transmitted at high voltages and low currents.
III) DC cannot be generated on such a large scale as to power cities.
IV) I2R power losses in transmission lines can be reduced with AC
V) AC voltage and current can be stepped up or down by transformers.
CIRCLE ONE OF THE ANSWERS BELOW FOR QUESTION 9.
A) I, III, V
B) II, III, V
C) III, IV, V
D) II, IV, V
10. The frequency at which the current alternates in the United States is
A) 120 Hz.
B) 100 Hz.
C) 240 Hz.
D) 60 Hz.
E) None of the above
11. Which statement is FALSE?
A) When applying Ohm’s law to AC RLC circuits the impedance takes the place of current.
B) The rms current Irms in an AC circuit is related to the maximum value of current Imax by .
C) Ampere’s law relates moving charges to magnetic fields.
D) The kWh is a unit of energy.
12. Consider an oscillating LC circuit. The energy in the capacitor is stored in the _____________. The energy in the inductor is stored in the ______________.
A) battery, battery
B) electric field, magnetic field
C) electric field, electric field
D) magnetic field, electric field
BONUSES:
Explain
1. Gauss’s law for charges
2. Gauss’s law for magnetism
3. Ampere’s law
4. Faraday’s law
Explanation / Answer
here,
Part 1:
Until it is magnetized, the atoms in a piece of iron are aligned in random directions and their tiny magnetic fields cancel each other out.
so option C is correct
Part 2:
From Lortez equation, F = q*v*B*SinA
Where Sin in angle betweeen field and force, so force will be maximum, when A = 90, sin90, Force, F = q*v*B
so option, C is correct
Part 3:
Magnatic field, B = uo*I/2*pi*r
Where,
uo is magantic permeability
I is current
r is distance to Wire
Option C is correct
Part 4:
option D is correct,
Part 5:
An electric motor is an electrical machine that converts electrical energy into mechanical energy.
Part 6:
The reverse of Electric motor would be the conversion of mechanical energy into electrical energy and is done by an electric generator.
Part 7:
Many electromagnetic coils have a magnetic core, a piece of ferromagnetic material like iron in the center to increase the magnetic field.
The current through the coil magnetizes the iron, and the field of the magnetized material adds to the field produced by the wire.
So, option C is correct
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