Currents and Circuits Unit

An engineer needs a 10 ohm resistor and a 15 ohm resistor. There are only 30 ohm resistors in stock, what should he do?

- Put two 30 ohm resistors in parallel for a 15 ohm resistor or three 30 ohm resistor in parallel for a 10 ohm resistor.

What four factors determine the amount of resistance that a wire will have?

- the length of the resistor (the longer the wire, the more resistance) - the cross sectional area of the resistor (the thinner, the more resistance) -the temperature of the resistor (the warmer, the more resistance) - the properties of the material (the fewer the number of free electrons, the more resistance)

Why is household wiring done in parallel instead of series?

1) In series, you'd need something plugged into every outlet for 1 to work. 2) With parallel, they have the same voltage in all the outlets. 3) Safety- can regulate current with fuses and circuit breakers

Explain the function of a fuse in an electric circuit

A fuse stops the current in case it gets too high. It melts to prevent a fire.

What is a short circuit? Why is a short circuit dangerous?

A short circuit is an area of low resistance (generally no resistance) connection between two points. It's dangerous because current is really high which may lead to fire.

Which wire conducts electricity with the least resistance? One with a large cross sectional diameter or one with a small cross sectional diameter?

A wire with a large cross sectional diameter conducts electricity with less resistance than a wire with a small cross sectional diameter because it's like water pipe pressure.

What causes an electric shock? Current or voltage?

Current

What is current?

Current is the flow of positive charge. It's measured in amperes and indicates the amount of charge that passes through a wire in one second.

If you have a 6V battery and many 1.5 volt bulbs, how could you connect them so they light but do not have more than 1.5 volts across each bulb?

Four light bulbs in series

Why is it dangerous to replace a 15 amp fuse in a circuit with a 30 amp fuse?

Its dangerous because you're increasing the threshold that current can be and higher currents can lead to fires.

Adding a resistor decreases total resistance in series or parallel circuits?

Parallel

If the current through one resistor goes to zero, the current through all other resistors will stay on in a series or parallel circuit?

Parallel

The voltage drop is the same across each resistors in series or parallel circuits?

Parallel

Are car headlights connected in series or parallel?

Parallel because if they were in series, if one burnt out, both would turn off.

Why is there a difference in total resistance between three 60 ohm resistors connected in series and three 60 ohm resistors connected in parallel?

Resistance is calculated in different ways for series and parallel circuits. In series, you add all the resistances up, and in parallel you take the inverse of the sum of the inverses.

Adding a resistor increases the total resistance in series or parallel circuits?

Series

If the current through one resistor goes to zero there is no current in the entire circuit in series or parallel circuits?

Series

The current is the same throughout in a series or a parallel circuit?

Series

The total resistance is equal to the sum of the individual resistances in a series or parallel circuit?

Series

The voltage drop is proportional to the resistance in series or parallel circuits?

Series

Several resistors with different values are connected in parallel. The equivalent resistance will be less than what resistor?

The equivalent resistance is smaller than the smallest resistor.

Home fires were often caused by people who replaced fuses with pennies. Why would this cause a problem?

They have no resistance so all the current goes through it and eventually it'll get really hot and melt.

What happens to the current in the other two lamps if one lamp in a three-lamp series circuit burns out?

They'll all go out because in series they're all in a row so if one goes out it causes an open circuit, meaning no current will flow because the resistance is infinity.

What happens to the current in the other two lamps if one lamp in a three-lamp parallel circuit burns out?

They'll get dimmer, because current will decrease because resistance increases when a resistor is removed.

What is voltage?

Voltage is the potential difference in an object or battery. To produce current, a difference in potential energy to lower potential. In an electrical circuit, the battery often is the source of potential difference.

What is resistance to current flow?

We refer to the friction that electrons encounter as resistance. Resistance slows down the electric charges and in the process causes wires or any other conductor of electricity to heat up.

Whys is it frustrating when one bulb burns out on a string of Christmas lights connected in series?

When one Christmas tree light burns out, all of them go out because there is an open circuit with a resistance of infinity.

Two 100 Watt light bulbs are connected in series to a 12 V battery and another two 100 W light bulbs are connected in parallel to a separate 12 V battery. Which battery will run out of energy first?

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