REVIEW HW ELECTRICITY
When the voltage across a certain resistance is V, the power delivered is P. If the voltage is doubled to V/2, the power delivered becomes
B. P/4.
The current with which a transformer is used
B. must be ac
A compass needle tends to
B.line up parallel to a magnetic field.
A transformer used to reduce 240-V ac to 120-V ac has an input current of 15 A. Its output current is
D. 30 A
The electric energy stored in a 6-V battery rated at 20 Ah is
D. 432 kJ.
THe mathematical form of coulombs law is similar to
Law of gravition
For an ohmic conductor, current is
inversely proportional to resistance
Earths magnetic field
is believe to arise from currents within planet's core
The voltage needed to produce a current of 8 A in a resistance of 12 ohms is
D. 96 V.
A magnet attracts
D. some substances and repels others.
Direct electric current cannot be used to operate
D. transformers
ELectricity charge is measure in units of..
coulombs
A generator is a device that converts
mechanical energy into electrical energy
The volt is the unit of electric
potential difference
Magnesium
results from the movement of electric charge
Direct electric current CAN be used
to operate electric motors
The electrical power dissipated in an appliance depends on
voltage,current,&resistance
In a conductor
electrons moves
If the voltage across a resistor doubles
the current doubles
The power rating of an electric motor that draws a current of 3 A when operated at 240 V is
720 watts
which would be the least conductive
Glass
If you rub a balloon on your sweater and then press it to a wall, it will often stick there. Why does this happen?
It Charges it electrostatically-induces opposite charge on wall
Which of the following are NOT true?
Protons and electrons have equal masses
The nucleus of an atom
contains most of the atoms mass
IF you were to cut a bar magnet in half
each piece would be small bar magnet with a north & south pole
Atoms and molecules are normally
electrically neutral
A ferromagnetic material loses this property above
the curie temp.
Ohm's law gives the relationship between
current and voltage
A motor converts
electrical energy into mechanical energy
Ohms law holds only
for metals
The current in a 24-W, 12-V light bulb is
2 A
A kilowatt hour is a unit of
A. energy
Electric Charge
B.occurs only in separate parcels of ±1.6 × 10-19 C.
The electrical force btw 2 objects depends on
(2 of the above) distance btw/charge of objects
a system w/ 8 E, and 4 neutrons has a charge of
-12.8x10^-19
a system of 16 E, 11 P, and 1 N has a net charge of
-8x10^-10 C
A component of an automobile 12-v electrical system has a resistance of 30. how much current?
.4A
Two 60-watt light bulbs are connected in parallel across a 120-V power line. The current in each bulb is
.5A
The current in a 20-ohm electric heater operating at 220-V is
12A
Three resistors 40, 60, & 50 are wired as a series and connect to a 120-V battery. WHat is equivalent resistance for this circuit?
150
Two charges, one positive and the other negative, are initially 2 cm apart and are then pulled away from each other until they are 8 cm apart. The force between them is now smaller by a factor of:
16
Two charges repel each other with a force of 10-6 N when they are 10 cm apart. When they are brought closer together until they are 2 cm apart, the force between them becomes
2.5 x 10-5 N.
AN insulator has a (+) charge of 4x10^-17 C. HOw many electrons were added/removed?
250 removed
The voltage needed to produce a current of 8 A in a resistance of 12 ohms is
96 volts
The primary coil of a transformer has 200 turns and its secondary coil has 50 turns, and the current in the secondary coil is 40 A. When a 12-V alternating current is applied to the primary coil of the transformer, the secondary voltage will be
A. 3 V
The primary coil of a transformer has 200 turns and its secondary coil has 40 turns. If the current in the secondary coil is 25 A, the current in the primary coil is
A. 5 A
Three 12-V batteries cannot be connected to give a voltage for the set of
A. 6 V
Atoms and molecules are normally
A. electrically neutral.
A current-carrying loop in a magnetic field always tends to turn until the plane of the loop is
A. parallel to the field.
A molecule that has lost an electron becomes a
A. positive ion
Relative to the electric force between two protons, the gravitational force between them is
A. weaker
The watt, the unit of power, is equal to the
A.(volt)(ampere).
Two 60-watt light bulbs are connected in parallel across a 120-V power line. The current in each bulb is
A.0.5 A.
When a current passes through a resistance, the electric energy that is lost
A.becomes heat.
When a magnetized iron bar is strongly heated, its magnetic field
A.becomes weaker.
The nucleus of an atom
A.contains most of the atom's mass.
Ohm's law
A.holds only for metals.
Coulomb's formula F = KQ1Q2/R2 gives the force between two charges in free space. The value of K
A.is the same under all circumstances.
Superconductivity occurs in certain substances
A.only at very low temperatures.
The current in a 20-ohm electric heater operated at 240 V is
B. 12 A
The current in a 24-W, 12-V light bulb is
B. 2 A
The power rating of an electric motor that draws a current of 3 A when operated at 240 V is
B. 720 W
An electric iron draws a current of 15 A when connected to a 120-V power source. Its resistance is
B. 8 ohms
A current-carrying wire is in a magnetic field with the direction of the current perpendicular to that of the field
B.The wire tends to move perpendicular to the field.
The electrons in an atom
B.are some distance away from the nucleus.
An object has a positive electric charge whenever
B.it has a deficiency of electrons.
The volt is the unit of electric
B.potential difference.
Two charges, one positive and the other negative, are initially 2 cm apart and are then pulled away from each other until they are 8 cm apart. The force between them is now smaller by a factor of
C. 16
The resistance of a 30-W, 12-V light bulb is
C. 2.5 ohms.
A magnet does not exert a force on
C. a stationary electric charge.
A current is flowing south along a power line. Neglecting the earth's field, the direction of the magnetic field under the power line is
C. east
A negative electric charge
C. interacts with both positive and negative charges.
Two charges of +Q are 1 cm apart. If one of the charges is replaced by a charge of -Q, the magnitude of the force between them is
C. the same
A charge of +Q attracts a charge of -Q 1 cm away with a force of F. Another charge of +Q is placed next to the first one. The force on the charge of -Q is now
C.2F
Which of the following statements is correct?
C.Moving electrons constitute electric currents.
When an observer moves past a stationary electric charge, she detects
C.both an electric and a magnetic field.
A drawing of the field lines of a magnetic field provides information on
C.both the direction and the strength of the field.
If undisturbed, an electric current in a superconducting wire loop
C.will continue indefinitely.
Two charges repel each other with a force of 10-6 N when they are 10 cm apart. When they are brought closer together until they are 2 cm apart, the force between them becomes
D. 2.5 × 10-5 N.
The primary coil of a transformer is connected to a source of alternating current of voltage V. The voltage of the secondary current is
D. Any of these choices could be correct, depending on the ratio of turns in the transformer coils.
A current-carrying wire is in a magnetic field with the direction of the current parallel to that of the field.
D. The wire has no tendency to move or to turn.
Which of the following statements is not true?
D.A proton in an atom circulates around its nucleus.
Which of the following statements is not true?
D.Protons and electrons have equal masses.
The conventional unit of battery capacity is the ampere-hour, which is actually a unit of
D.electric charge.
In a battery circuit w/ different resistors in parrellel..
The voltage is the same across each resistor
If work is done on an electrical charge
a voltage is present
A current flowing thru a copper wire (which is connect to a battery) is due to
electrons being accelerated by an electric field
A kilowatt hour is in units of
energy
If 2 macroscopic objects are electrically attracted to each other
one object is (-) & the other is (+)
If a (-) object is brought near a suspended, (+) object, the suspended obect
will be attracted
A system of an electron, a proton, and a neutron has a net charge of
zero