# Does This Material Follow Ohm's Law?

• physicsphobic
In summary, the conversation is about a person seeking urgent help with introductory physics questions. They ask for help with various problems involving voltage, current, power, and energy. The conversation ends with the person figuring out most of the problems themselves.
physicsphobic
urgently needed help on intro physics...

This is my first time posting on here so I hope someone will answer my questions.

Here they are:

1. A scientist testing a material discovers that when a voltage of 10V is placed across a material a current of 10A flows. When a voltage of 20V is placed across it, however, a current of 15A flows through it. Does this material obey Ohm's law? Give reason for your answer.

2.a. How much power does a light bulb connected to a 120V outlet use if if draws 0.5A of current? My answer is: 120V *0.5A= 60W
b. One kilowatt-hour is a measure of energy which is equal to 3,600,000J. How many hours would you have to leave on the light bulb from part a in order to expend one kilowatt-hour of energy?

c. If one kilowatt-hour costs $.10, how long would you have to leave the light bulb from part a on in order to spend$1.00 on electricity?

3. The electric charge of an electron is -1.6x10^-19C. What is the force exerted between two electrons separated by one meter? (Be sure to note whether the force is attractive or repulsive).

Thanks for any help given to this newbie!

Joanne

Welcome to PF!

Hi Joanne! Welcome to PF!

For the others, show us what you've tried, and where you're stuck, and then we'll know how to help!

OK, since nobody wants to give me the answers I'll try to give what I think are the answers and, hopefully someone will be kind enough to give me the correct answers.

Since 2a is correct, here's what I think about 2b:
according to my textbook I use this formula..energy=power * time.
plugging the 3,600,000J in for energy and 60W in for power I get: 3600000=60W * time
leaving time on one side, time=60W/3600000=60,000 hours? Is this right because my algebras a little rusty.

2c has me stumped so any help is greatly appreciated.
The first question I think it does obey ohms law because the greater the resistance, the less the current and if the resistance is doubled the current will be half what it would be otherwise. Right??

Hi Joanne!

Sorry, but on this forum we don't give you the answers.
physicsphobic said:
Since 2a is correct, here's what I think about 2b:
according to my textbook I use this formula..energy=power * time.
plugging the 3,600,000J in for energy and 60W in for power I get: 3600000=60W * time
leaving time on one side, time=60W/3600000=60,000 hours? Is this right because my algebras a little rusty.

Why are you using 3,600,000?

The question asks for 1 kWhr, (that's the same power as a kW heater for an hour) … joules have nothing to do with it.

Try again.
The first question I think it does obey ohms law because the greater the resistance, the less the current and if the resistance is doubled the current will be half what it would be otherwise. Right??

Ohm's law mentions the amount of the resistance … how much is the resistance in this case?

tiny-tim said:
Sorry, but on this forum we don't give you the answers.

We also have forums specifically for getting help with homework / coursework exercises. They're sub-forums of "Homework & Coursework Questions" which is near the top of the list of forums. I've moved this thread to "Introductory Physics."

figured out most of the problems myself so thanks anyway, tiny-tim for your "help".

physicsphobic said:
figured out most of the problems myself so thanks anyway, tiny-tim for your "help".

you're welcome … we always think our "help" is most successful when the OP ends up answering the question him/herself

## 1. What is the basic concept of physics?

The basic concept of physics is the study of matter and its motion through space and time, as well as the forces and energy that affect it.

## 2. What topics are typically covered in an introductory physics course?

An introductory physics course typically covers topics such as motion, forces, energy, waves, electricity, and magnetism.

## 3. How can I improve my understanding of physics?

Some ways to improve your understanding of physics include practicing problems, seeking help from a tutor or teacher, and engaging in hands-on experiments or demonstrations.

## 4. What are some common misconceptions about physics?

Some common misconceptions about physics include thinking that everything is either a solid, liquid, or gas, when in reality there are many other states of matter, and believing that objects always fall at the same rate regardless of their mass, when in fact heavier objects fall faster due to gravity.

## 5. How does physics relate to everyday life?

Physics plays a role in many aspects of everyday life, such as the functioning of electronic devices, the laws of motion used in driving a car, and the principles of heat and thermodynamics in cooking. Understanding physics can also help in problem-solving and critical thinking skills.

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