Short Circuit
What happens when you blow a fuse?
Current flowing through a wire heats the wire. The length of a wire affects its resistance, which determines how much current flows in the wire and how hot the wire gets.
Materials
A fresh 6-volt or 12-volt lantern battery.
A length of copper wire with alligator clips attached to each end (or a test lead) from any electronics supply store. A strand of very fine iron wire, about 5 to 6 inches (13 to 15 cm) long. (You can get this by unbraiding a short length of picture-hanging wire or any braided iron wire.)
Adult help
Assembly
(5 minutes or less)
(1) Attach one end of the clip lead to one of the battery terminals. Attach one end of the fine iron wire to the other terminal. Attach the other end of the clip lead to the other end of the iron wire, placing the clip as far from the terminal as possible.
To Do and Notice
(15 minutes or more)
(2) Observe what happens to the iron wire after you connect the clip. Move the clip on the iron wire a little closer to the battery and watch what happens. Keep moving the lead closer until you see the final dramatic result. (CAUTION: The wire gets very hot!)
What's Going On?
(3) The thin iron wire is a good conductor of electricity, but not as good as the copper wire, which is deliberately chosen to have very low resistance. Thus, most of the resistance of the circuit is in the iron wire. When you connect the clip to the iron wire, the voltage of the battery pushes electrons through the circuit against the resistance of the iron wire, causing the iron wire to heat up. As you move the clip closer to the battery, the resistance of the iron wire decreases. Because the same voltage is applied across a lower resistance, more current flows, and the wire heats up more. Eventually, when you make the iron wire short enough, so much current flows that it melts the wire. Even the copper wire becomes warm.
(4) In a normal electric circuit, an electric current powers an appliance, such as a refrigerator or TV. Every such appliance has a certain amount of resistance to the current flow, which keeps the current from reaching very large values. A short circuit occurs when the current finds a way to bypass the appliance on a path that has little or no resistance—for example, where frayed insulation bares a wire and allows it to touch the frame of the appliance, so the current can flow straight to the ground. In this situation, a very large current can occur, producing a lot of heat and a fire hazard.
(5) Although houses today often contain circuit breakers rather than fuses, fuses are still around. A fuse contains a thin strip of wire, somewhat like the thin iron wire in our experiment. The current that goes to appliances must also pass through this strip of wire. If a short circuit occurs—or even if too many appliances get hooked up to one wire, so that too much current flows—the wire in the fuse heats up quickly and melts, breaking the circuit and preventing a fire from breaking out.
Question 1
Part A
Which sentence best states a central idea of "Short Circuit"?(1 point)
Responses
The flow of electrons follows a path of least resistance.
The flow of electrons follows a path of least resistance.
Appliances can be destroyed by a heavy flow of electrons.
Appliances can be destroyed by a heavy flow of electrons.
Circuit breakers are a tool to control the flow of electricity in homes.
Circuit breakers are a tool to control the flow of electricity in homes.
Fuses are an important means to keep homes safe from electrical hazards.
Fuses are an important means to keep homes safe from electrical hazards.
Question 2
Part B
Which detail from the article provides the best example of the central idea in Part A?(1 point)
Responses
"In a normal electric circuit, an electric current powers an appliance, such as a refrigerator or TV."
"In a normal electric circuit, an electric current powers an appliance, such as a refrigerator or TV."
". . . the wire in the fuse heats up quickly and melts, breaking the circuit and preventing a fire from breaking out."
". . . the wire in the fuse heats up quickly and melts, breaking the circuit and preventing a fire from breaking out."
"Every such appliance has a certain amount of resistance to the current flow, which keeps the current from reaching very large values."
"Every such appliance has a certain amount of resistance to the current flow, which keeps the current from reaching very large values."
"Although houses today often contain circuit breakers rather than fuses, fuses are still around."
"Although houses today often contain circuit breakers rather than fuses, fuses are still around."
Question 1:
The sentence that best states a central idea of "Short Circuit" is: Fuses are an important means to keep homes safe from electrical hazards.
Question 2:
The detail from the article that provides the best example of the central idea in Part A is: "The wire in the fuse heats up quickly and melts, breaking the circuit and preventing a fire from breaking out."
Short Circuit
What happens when you blow a fuse?
Current flowing through a wire heats the wire. The length of a wire affects its resistance, which determines how much current flows in the wire and how hot the wire gets.
Materials
A fresh 6-volt or 12-volt lantern battery.
A length of copper wire with alligator clips attached to each end (or a test lead) from any electronics supply store. A strand of very fine iron wire, about 5 to 6 inches (13 to 15 cm) long. (You can get this by unbraiding a short length of picture-hanging wire or any braided iron wire.)
Adult help
Assembly
(5 minutes or less)
(1) Attach one end of the clip lead to one of the battery terminals. Attach one end of the fine iron wire to the other terminal. Attach the other end of the clip lead to the other end of the iron wire, placing the clip as far from the terminal as possible.
To Do and Notice
(15 minutes or more)
(2) Observe what happens to the iron wire after you connect the clip. Move the clip on the iron wire a little closer to the battery and watch what happens. Keep moving the lead closer until you see the final dramatic result. (CAUTION: The wire gets very hot!)
What's Going On?
(3) The thin iron wire is a good conductor of electricity, but not as good as the copper wire, which is deliberately chosen to have very low resistance. Thus, most of the resistance of the circuit is in the iron wire. When you connect the clip to the iron wire, the voltage of the battery pushes electrons through the circuit against the resistance of the iron wire, causing the iron wire to heat up. As you move the clip closer to the battery, the resistance of the iron wire decreases. Because the same voltage is applied across a lower resistance, more current flows, and the wire heats up more. Eventually, when you make the iron wire short enough, so much current flows that it melts the wire. Even the copper wire becomes warm.
(4) In a normal electric circuit, an electric current powers an appliance, such as a refrigerator or TV. Every such appliance has a certain amount of resistance to the current flow, which keeps the current from reaching very large values. A short circuit occurs when the current finds a way to bypass the appliance on a path that has little or no resistance—for example, where frayed insulation bares a wire and allows it to touch the frame of the appliance, so the current can flow straight to the ground. In this situation, a very large current can occur, producing a lot of heat and a fire hazard.
(5) Although houses today often contain circuit breakers rather than fuses, fuses are still around. A fuse contains a thin strip of wire, somewhat like the thin iron wire in our experiment. The current that goes to appliances must also pass through this strip of wire. If a short circuit occurs—or even if too many appliances get hooked up to one wire, so that too much current flows—the wire in the fuse heats up quickly and melts, breaking the circuit and preventing a fire from breaking out.
Question 1
Part A
Which paragraph best summarizes the conclusions of the experiment in "Short Circuit"?(1 point)
Responses
paragraph 2
paragraph 2
paragraph 3
paragraph 3
paragraph 4
paragraph 4
paragraph 5
paragraph 5
Question 2
Part B
Identify three details from "Short Circuit" that provide the best summary of the conclusions in the experiment.(1 point)
Responses
Most houses have circuit breakers.
Most houses have circuit breakers.
Frayed wires can touch appliances.
Frayed wires can touch appliances.
Iron wire is a good conductor of electricity.
Iron wire is a good conductor of electricity.
The length of a wire affects its resistance.
The length of a wire affects its resistance.
Electric current powers appliances.
Electric current powers appliances.
A short circuit occurs when there is a high flow of current with low resistance.
A short circuit occurs when there is a high flow of current with low resistance.
Appliances can short-circuit, creating a fire hazard.
Question 1:
The paragraph that best summarizes the conclusions of the experiment in "Short Circuit" is: paragraph 5.
Question 2:
The three details from "Short Circuit" that provide the best summary of the conclusions in the experiment are:
- Iron wire is a good conductor of electricity.
- The length of a wire affects its resistance.
- A short circuit occurs when there is a high flow of current with low resistance.
from "The President's Speech to Students"
(1) You’re this country’s future. You’re young leaders. And whether we fall behind or race ahead as a nation is going to depend in large part on you. So I want to talk to you a little bit about meeting that responsibility.
(2) It starts, obviously, with being the best student that you can be. Now, that doesn’t always mean that you have to have a perfect score on every assignment. It doesn’t mean that you’ve got to get straight As all the time—although that’s not a bad goal to have. It means that you have to stay at it. You have to be determined and you have to persevere. It means you’ve got to work as hard as you know how to work. And it means that you’ve got to take some risks once in a while. You can’t avoid the class that you think might be hard because you’re worried about getting the best grade if that’s a subject that you think you need to prepare you for your future. You’ve got to wonder. You’ve got to question. You’ve got to explore. And every once in a while, you need to color outside of the lines.
(3) That's what school is for: discovering new passions, acquiring new skills, making use of this incredible time that you have to prepare yourself and give yourself the skills that you’re going to need to pursue the kind of careers that you want. And that’s why when you’re still a student you can explore a wide range of possibilities. One hour you can be an artist; the next, an author; the next, a scientist, or a historian, or a carpenter. This is the time where you can try out new interests and test new ideas. And the more you do, the sooner you’ll figure out what makes you come alive, what stirs you, what makes you excited—the career that you want to pursue. . .
(4) So that’s a big part of your responsibility, to test things out. Take risks. Try new things. Work hard. Don’t be embarrassed if you’re not good at something right away. You’re not supposed to be good at everything right away. That's why you’re in school. The idea, though, is that you keep on expanding your horizons and your sense of possibility. Now is the time for you to do that. And those are also, by the way, the things that will make school more fun.
(5) Down the road, those will be the traits that will help you succeed, as well—the traits that will lead you to invent a device that makes an iPad look like a stone tablet. Or what will help you figure out a way to use the sun and the wind to power a city and give us new energy sources that are less polluting. Or maybe you’ll write the next great American novel. . . .
(6) But I also want to emphasize this: With all the challenges that our country is facing right now, we don’t just need you for the future; we actually need you now. America needs young people’s passion and their ideas. We need your energy right now. I know you’re up to it because I’ve seen it. Nothing inspires me more than knowing that young people all across the country are already making their marks. They're not waiting. They're making a difference now. . . .
Question 1
Which of the following words or phrases provide the best context to determine the meaning of "pursue" as it is used in paragraph 3 of the passage?(1 point)
Responses
"...kind of careers that you want."
"...kind of careers that you want."
"...with being the best student you can be..."
"...with being the best student you can be..."
"...determined..."
"...determined..."
"...work as hard as you know how to work."
"...work as hard as you know how to work."
Question 2
Which of the following words could replace responsibility in the following sentence to retain the original meaning but add a more serious/formal connotation?
"So I want to talk to you a little bit about meeting that responsibility."(1 point)
Responses
evidently
evidently
obligation
obligation
immaturity
immaturity
vaguely
vaguely
Question 3
Which of the following words could complete the following analogy:
freezing is to melting as pursue is to _____
(1 point)
Responses
chase
chase
neglect
neglect
like
like
dodge
dodge
Question 4
What evidence from the speech best shows how students can prepare themselves for the future?(1 point)
Responses
Students need to act responsibly during their time in school.
Students need to act responsibly during their time in school.
Students should focus on courses that will help them earn good grades.
Students should focus on courses that will help them earn good grades.
Students should realize that they will not excel at everything that they try.
Students should realize that they will not excel at everything that they try.
Students need to try new possibilities to discover what excites them.
Students need to try new possibilities to discover what excites them.
Question 5
Which sentence from the passage BEST supports the idea that President Obama thinks students must take responsibility for their own future?(1 point)
Responses
"Now, that doesn't always mean that you have to have a perfect score on every assignment."
"Now, that doesn't always mean that you have to have a perfect score on every assignment."
"Down the road, those will be the traits that will help you succeed, as well - the traits that will lead you to invent a device that makes an iPad look like a stone tablet."
"Down the road, those will be the traits that will help you succeed, as well - the traits that will lead you to invent a device that makes an iPad look like a stone tablet."
"Your first obligation is to make sure that you're preparing yourself for college and career."
"Your first obligation is to make sure that you're preparing yourself for college and career."
"Soon enough, you will be the ones leading our businesses and leading our government."
"Soon enough, you will be the ones leading our businesses and leading our government."
Question 6
Which of the following statements best expresses the central idea of the passage?(1 point)
Responses
President Obama addresses students because he is concerned that they are not taking school seriously and that the country will fall behind as a result.
President Obama addresses students because he is concerned that they are not taking school seriously and that the country will fall behind as a result.
President Obama congratulates students for their work in school and attributes America's success to their determination.
President Obama congratulates students for their work in school and attributes America's success to their determination.
President Obama chastises the students of America for their lack of perseverance and their immaturity.
President Obama chastises the students of America for their lack of perseverance and their immaturity.
President Obama encourages students to take their responsibility as America's future seriously by being the best student they can be.
President Obama encourages students to take their responsibility as America's future seriously by being the best student they can be.
Question 7
Which of the following pieces of evidence BEST supports the idea that academic achievements are not the only way to measure success?(1 point)
Responses
"It starts, obviously, with being the best student that you can be."
"It starts, obviously, with being the best student that you can be."
"That's what school is for: ...making use of this incredible time that you have to prepare yourself and give yourself the skills that you’re going to need."
"That's what school is for: ...making use of this incredible time that you have to prepare yourself and give yourself the skills that you’re going to need."
"Now, that doesn’t always mean that you have to have a perfect score on every assignment. It doesn’t mean that you’ve got to get straight As all the time."
"Now, that doesn’t always mean that you have to have a perfect score on every assignment. It doesn’t mean that you’ve got to get straight As all the time."
"Nothing inspires me more than knowing that young people all across the country are already making their marks."
"Nothing inspires me more than knowing that young people all across the country are already making their marks."
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Question 1:
The phrase "kind of careers that you want" provides the best context to determine the meaning of "pursue" as it is used in paragraph 3 of the passage.
Question 2:
The word "obligation" could replace "responsibility" in the sentence to retain the original meaning but add a more serious/formal connotation.
Question 3:
The word "chase" could complete the following analogy: freezing is to melting as pursue is to chase.
Question 4:
The evidence from the speech that best shows how students can prepare themselves for the future is: Students need to try new possibilities to discover what excites them.
Question 5:
The sentence "Your first obligation is to make sure that you're preparing yourself for college and career." BEST supports the idea that President Obama thinks students must take responsibility for their own future.
Question 6:
The statement that best expresses the central idea of the passage is: President Obama encourages students to take their responsibility as America's future seriously by being the best student they can be.
Question 7:
The evidence that BEST supports the idea that academic achievements are not the only way to measure success is: "Nothing inspires me more than knowing that young people all across the country are already making their marks."
Question 1:
The sentence that best states a central idea of "Short Circuit" is: Fuses are an important means to keep homes safe from electrical hazards.
Question 2:
The detail from the article that provides the best example of the central idea is: "The wire in the fuse heats up quickly and melts, breaking the circuit and preventing a fire from breaking out."
To determine the answer to Part A, we need to identify the central idea of the article "Short Circuit." We can do this by summarizing the main point or theme discussed in the article. In this case, the article explains how a short circuit occurs when the current in an electric circuit finds a path with little or no resistance, leading to a large current flow, heat production, and a potential fire hazard. The article also mentions that fuses are important safety measures as they contain a wire that melts when too much current flows, breaking the circuit and preventing a fire.
Based on this information, the central idea of the article is that fuses are an important means to keep homes safe from electrical hazards. Therefore, the correct answer to Part A is: Fuses are an important means to keep homes safe from electrical hazards.
To answer Part B, we need to find a detail from the article that provides an example of the central idea stated in Part A. In this case, the detail that best exemplifies the central idea is the statement "the wire in the fuse heats up quickly and melts, breaking the circuit and preventing a fire from breaking out." This detail demonstrates how a fuse functions to protect against electrical hazards by breaking the circuit when the wire heats up and melts due to excessive current flow.
Therefore, the correct answer to Part B is: "The wire in the fuse heats up quickly and melts, breaking the circuit and preventing a fire from breaking out."