### 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**