Block 5

You put two identical D-cells (1.5 V) together: the positive terminal of one battery, in direct contact with the positive terminal of a second battery. The electric potential between the negative terminal of the first battery, and the negative terminal of the second battery (eg. the two free ends) is

0 Volts.

A positive 2 milli-coulomb charge is next to a positive 1 milli-coulomb charge. At a particular distance, the 1 milli-coulomb charge feels a repulsive force of 2 Newtons. If the distance between the charges is doubled, then the 1 milli-coulomb charge should feel a force of:

1/2 Newton

If the distance between two electric charges is doubled, then the force they exert on each other changes by how much?

1/4 as large

You put two identical D-cells (1.5 V) together: the positive terminal of one battery, in direct contact with the negative terminal of a second battery. The electric potential between the negative terminal of the first battery, and the positive terminal of the second battery (eg. the two free ends) is

3.0 Volts.

An uncharged metal ball is placed on an insulating stand and a positively charged rod is brought close (but not touching) to it. For the metal ball:

A negative charge is induced on the surface closest to the rod, and a positive charge is induced on the surface farthest away from the rod

What is a photoconductor?

A normally insulating material that becomes a conductor while exposed to light.

Your flashlight has three identical 1.5 volt batteries in it, arranged in a chain to give a total of 4.5 volts. Current passes first through battery (a), then through battery (b), then through battery (c), on its way to the bulb. When you operate the flashlight, the batteries provide power to the current and they gradually use up their chemical potential energy. Which battery will run out of chemical potential energy first?

All three will run out at the same time.

You are walking on a carpet in your socks during the winter. What can you do to keep yourself from getting shocked when you touch the doorknob?

Hold a pin in your hand so that the corona can dissipate charge into the air.

What purpose does a fuse serve?

In the event that too much current is flowing in the circuit, a fuse will blow causing an open circuit, stopping the flow of current.

When handling integrated circuits such as memory chips, you are often advised to wear a wrist-strap which is connected to ground. This is because:

It insures you don't carry a charge. Static discharge through such integrated circuits would ruin the chips.

The resistance of the power wires that lead from your toaster oven to the wall, in comparison to the resistance of the coils that get hot and glow inside the oven, is

Lower

Two uncharged metal balls are placed on insulating stands and connected with a copper wire. A positively charged rod is brought close (but not touching) to one of the balls and the wire is cut. Afterwards,

The ball closest to the rod becomes negatively charged and the ball farthest away becomes positively charged.

You shuffle your feet on the carpet on a winter day and build up charge on your body. Where does that charge reside?

The charge resides on the surface of your body because like charges repel one another.

The flame of a candle is observed to stream towards an operating Van deGraff generator. This shows that

The flame contains charged ions.

A large battery powers your portable radio. Current enters the radio through the red wire and leaves through the black wire. Which wire is at higher voltage?

The red wire.

A sock is negatively charged with -0.0000001 C (10 -7 C). Since a single electron has a charge of 1.6 x 19 -19 C, this means that there are at least 10 12electrons on the sock. Which statement is true about the sock?

The sock has 1012 too many electrons on it.

Lint collects on your sweaters in the winter because

Your sweater becomes positively charged, and lint becomes polarized and sticks to your sweater.

The photoconductor used in a xerographic copier

does not conduct electrical current in the dar

A positively charged object is able to attract

both negatively charged and neutral objects.

Your cat has chewed the cord to your desk lamp and has created a short circuit—an electric connection from one wire to the other inside the cord. When you plug the lamp into the electric outlet,

current will bypass the bulb and the bulb will not light up.

Suppose that you reverse the two batteries in an ordinary flashlight and that they make good contact with the flashlight's wires. If you now turn on the flashlight,

current will run backward through the flashlight's circuit but the bulb will light up normally.

Your car has a dead battery. To properly jump start your car you should connect

first the positive terminal of the good battery to the positive terminal of the dead battery. Then you should connect the negative terminal of the good batter to any metal part of the car with the dead battery.

You have just pulled your clothes from the dryer and find that a sock is clinging to your jeans with static electricity. You hold the jeans in one hand and the sock in the other and pull the two apart. As the jeans and sock move apart, the forces between them become weaker because the

forces between electric charges become weaker with increasing distance.

Three D-cells are placed into a 4.5 Volt flashlight but the middle battery is inserted backwards. The light

glows dimly and the middle battery charges

In the dark, the photoconductors used in most xerographic copiers are

insulators.

The surface of a photoconductor has been coated with electric charge. This charge will remain in place until you expose the surface to

light.

In an open circuit,

no current flows.

A rocking chair has damaged the cord of your desk lamp. One of the two wires in the cord is completely cut in half and cannot carry any current. However, the other wire still connects the lamp to the electric socket. If you turn on the lamp,

no current will flow through either wire and the lamp will remain dark.

A negatively charged metal sphere contains too many electrons. These extra electrons reside

on the surface of the sphere.

The surface of a photoconductor is covered with negatively charged electrons which form an interesting pattern on its surface. In order to get ink to stick to the surface, the ink must be

positively charged.

A battery

pumps positive charge from its negative terminal to its positive terminal.

You stick two pieces of adhesive tape on a glass window and then pull them off suddenly. If you now hold the tape pieces near each other, they will be

repelled because they have like charges.

When the copies emerge from a xerographic copier, they tend to stick to things and attract lint. What causes this effect?

the charge that was placed on the paper to attract the toner is not always removed completely and the toner itself is charged.

If you walk on a carpet and become negatively charged, you can avoid the shocks of static electricity by carrying a very sharp needle in your hand and holding it out before touching a metal doorknob or wall. How does that needle protect you from static electricity?

the needle emits negative charge into the air via a corona discharge.

A capacitor consists of two metal surfaces separated by an insulating layer. A new capacitor has no charge on either of its surfaces. If you begin transferring charge from one surface to the other, the first surface becomes negatively charged while the second surface becomes positively charged. As you transfer the charge, the voltage of

the positively charged surface increases and the energy stored in the capacitor increases.

If you take a sweater off in the dark you can see a bright display of sparks flashing from the sweater to your shirt. This happens because

the sweater becomes positively charged and you become negatively charged.

A negatively charged sock fresh from the dryer can stick to a wall quite easily. This occurs because

the wall is polarized by the presence of the negatively charged sock.

After combing your hair on a hot dry day, you do the experiment described in the book and find your comb can attract a stream of water because

the water molecules, although neutral, are electric dipoles (they are polarized) and are attracted to the charge on the comb.

You have just built a house out in the country and it comes to your attention that you need to install a lightning rod. Being naturally curious you ask a hardware salesperson how lightning rods work and they correctly tell you that

they produce corona discharges that diminish any local buildups of electrical charge.

Two metal plates are separated by air (a good insulator) and the top plate is charged positively while the bottom plate is charged negatively. An electron from the electron gun of a TV shoots from left to right through the two plates. Assuming the top plate is positively charged and the bottom plate is negatively charged, in which direction will the negatively charged electron deflect while in between the plates?

up

You are standing on a plastic bench that insulates you from your surroundings. Both you and the helium balloon you are holding are electrically neutral. You now rub the balloon against your sweater, so that the balloon becomes negatively charged, and then let the balloon float away. You are left

with a positive electric charge.

A wire carries 1 Ampere of current or 1 Coulomb/Sec, If you were able to look closely at the interior of the wire you see

~1018 elecrons/second.