# Physics Ch. 15

## 40 terms

coulomb

### An object is___when it has equal numbers of positive and negative charges.

electrically neutral

### ___exists when there is an excess of one type of charge on an object.

static electricity

Coulomb's law

### ____occurs when clothes brush against each other in the dryer.

charging by friction

electroscope

induction

### What does it mean to say an object is electrically neutral?

An object is electrically neutral when its net charge is zero.

### How does the charge of an electron compare to the charge of a proton?

The charge of an electron is equal to the charge of a proton with the opposite sign.

### Why don't you usually notice electric forces between objects?

Because most objects are electrically neutral.

### What two factors determine the amount of electric force between two objects?

the size of the charges and the distance between the charges

### What happens to the force between two charges as they are moved closer together?

The force between the charges gets stronger.

### Explain what happens to the force between two protons if each of the following occurs: The distance between them is cut in half.

force increases by four times

### Explain what happens to the force between two protons if each of the following occurs: The distance between is doubled.

the force decreases by four times

### Explain what happens to the force between two protons if each of the following occurs: The distance between them is tripled.

the force decreases by nine times

### Explain what happens to the force between two protons if each of the following occurs: One of the protons is replaced with an electron.

the force becomes attractive

### Explain what happens to the force between two protons if each of the following occurs:One of the protons is replaced with two electrons.

force is attractive and increases by two times

### What happens to the charges in your hair and a balloon if you rub them together?

hair will become positively charged; balloon will become negatively charged

### ___is when you rub a balloon on your hair.

charging by friction

field lines

polarized

electric field

### How are the units ampere and coulomb related?

amperes are coulombs per second

### Ben Franklin defined current as going from ______. Now we know that electrons in a circuit move from ___.

positive to negative; negative to positive

### Do all the electrons in a wire move to make the current in a circuit?

no, only the valence electrons move

No

### Why can current easily be created in a conductor but not in an insulator?

Because conductors have electrons that are free to move and insulators do not.

### One volt equals one ___of energy per __of charge. A volt is also equal to one ____of power per___of current.

joule, coulomb; watt, ampere

capacitor

farads

### What is a capacitor?

A capacitor is a device that stores electrical energy in a circuit.

### What use do capacitors have?

A charged capacitor can create current in a circuit.

### What does it mean to say a capacitor is charged?

A capacitor is charged when one plate is positively charged and the other is negatively charged.

### What happens to the current in a circuit as a capacitor charges?

The current in a circuit containing a capacitor decreases to zero as the capacitor charges.

### Which three factors affect a capacitor's capacitance?

the distance between the plates; the area of the plates; the insulating material between the plates

106.2 Coulombs

-1.602E-18 C

1.49e+19

6.24E18

### What is the formula for current? Voltage?

Coulomb/sec; joules/coulomb