Chapter 12-14 Positive And Negative Charge – Physics
This chapters covers Positive And Negative Charge – Physics.
When a glass rod rubbed with silk acquires a positive charge, the silk acquires
a negative charge
A rod with a positive charge is brought near a positively charged pith ball. The pith ball is suspended from an insulating string. The pith ball will be
repelled by the rod
If the distance between two point charges is doubled while the size of the charges remains the same, the force between the charges is multiplied by
0.25
If the distance between two point charges remains constant while the size of one of the charges is doubled, the force between the charges is multiplied by
2
Materials that allow electric charges to move freely are called
conductors
The unit for electric charge is
Coulomb
Electric field lines are envisioned as
radiating inward toward a negative charge and out of a positive charge.
The normal tendency of positive charges is to
move to regions of lower electric potential
The change in electric potential is equal to the
the change in electrostatic energy divided by the amount of the charge
The unit for electric potential is
Volt
Electrical current is
the charge per unit time
The unit for electrical current is
Amperes
Electrical resistance is
the property of a circuit element that opposes the flow of current
The unit of electrical resistance is
ohms
Resistances connected in series all have
the same current
Resistances connected in parallel all have
the same potential difference
Power supplied by a battery is calculated as
the potential difference times the current
The power dissipated by a resistance may be calculated as
the square of the current times the resistance
A voltmeter is always connected
in parallel with the circuit element whose potential difference is to be measured
Household circuits are wired in
parallel to an alternating current source
like charges repel each other and opposite charges
attract
what are some examples of conductors ?
metals, like copper, silver, iron, gold; our bodies
what is an insulator ?
Materials that do not ordinarily permit charge to flow
what are some examples of insulators?
plastic; glass; ceramics; other nonmetallic materials
what is a semiconductor?
are intermediate between a good conductor and a good insulator
what is an electric dipole?
the center of the negative charge is slightly displaced from the center of the positive charge
polarized
who measured how the electrostatic force varies with distance and quantity of charge?
Coulomb
The electrostatic force between two charged objects is proportional to the quantity of each of the charges and inversely proportional to what?
the square of each distance between the charges
The electrostatic force has the same inverse-square dependence on distance as what?
Newton’s Law of Gravitation
If we double the distance between the charges, the force falls to
one -fourth of the original
what is the electric force per unit positive charge that would be exerted on a charge if it were placed at that point?
the electric field
what are field lines used for?
a means of visualizing both the direction and strength of the field
two charges of equal magnitude but opposite sign, separated by a small distance is what?
an electric dipole
what kind of force is an electrostatic force?
conservative
Electric potential and potential energy are closely related BUT
they are not the same
If the charge q is negative, its potential energy will __________________when it is moved in the direction of increasing electric potential.
decrease
For a uniform electric field, there is a simple relationship between the magnitude of the electric field and the change in electric potential: what is it?
changeV = Ed
what is a semiconductor?
are intermediate between a good conductor and a good insulator
what are some examples of conductors ?
metals, like copper, silver, iron, gold; our bodies
what are some examples of conductors ?
metals, like copper, silver, iron, gold; our bodies
The magnetic field lines produced by a current in a straight wire
are directed in concentric circles around the wire.
Electrons flow around a circular wire loop in a horizontal plane, in a direction that is clockwise when viewed from above. This causes a magnetic field. Inside the loop, the direction of this magnetic field is
up.
The north pole of a magnetic compass needle points towards the north geographic pole of the Earth because
there is a south magnetic pole near the north geographic pole.
Which of the following cannot induce a current in a loop of wire?
A stationary magnet inside the stationary loop.
Two long bar magnets are aligned so that north poles face each other. The magnets are separated by 1 cm, and a repulsive force between the north poles is 0.080 N. When the separation is increased to 2 cm the force will be
0.020 N
Imagine a magnetic field pointing into the plane of this page (screen). An electron moves across the page (screen) from left to right. The direction of the magnetic force on the electron will be
toward the bottom of the page (screen).
A transformer has 200 turns on the primary coil and 20 turns on the secondary coil. The primary coil is connected to a direct current source of 100 millivolts. The voltage in the secondary coil will be
zero
A bar magnet is broken in half and the magnetic field around one piece is mapped out. What is wrong with this picture?
There is no south pole.
High AC voltages are desirable for long distance transmission of electric power because
the higher the voltage the lower the current, which reduces the power lost.
What does the sign of position (x or y) tell you about an object?
where an object is
What does the sign of velocity (v_x or v_y) tell you about an object?
which direction the object is moving
What does the sign of acceleration (a_x or a_y) tell you about an object?
which way the acceleration vector points (NOT speeding up of slowing down)
Longer velocity vectors symbolize…
faster speed
Shorter velocity vectors symbolize…
slower speed
When an acceleration vector and a velocity vector point in the same direction an object…
is speeding up
When an acceleration vector and a velocity vector point in different directions an object…
is slowing down
An object is speeding up if and only if…
v_x and a_x have the same sign
An object is slowing down if and only if…
v_x and a_x have opposite signs
An object’s velocity is constant if and only if…
a_x = 0
In position-versus-time graphs a steep slope means…
higher velocity
In position-versus-time graphs a negative slope means…
negative velocity; motion to the left (or down)
Define speed
how fast and object is moving, independent of direction
What is the difference between average velocity and instantaneous velocity?
average velocity has a change in time; instantaneous velocity is the slope of the tangent line at time t
Where is the “turning point” on a velocity-versus-time graph?
the point at which x ( v(t)=0 ) + x_0.
dx=
vxt
dy=
vyit+1/2at^2
vyi=
vi sin Θ
vxi=
vi cos Θ
vf=
vi+at
vf^2=
vi^2+2ad
v=
d/t
d=
1/2at^2
a^2+b^2=
c^2
sin Θ
opposite/hypotenuse
cos Θ
adjacent/ hypotenuse
tan Θ
opposite/ adjacent