by Ron Kurtus
Readers have sent in a total of 796 comments and questions on Physics issues. They are listed according to date.
You can read them to further your understanding of the subject.
|Equation different in textbook||Doppler Effect||India|
|Using static electricity to charge phone||Basics of Static Electricity||Egypt|
|Uses for friction||Uses of Friction||Nigeria|
|References on electrostatic painting||Uses for Static Electricity||Egypt|
|New Triboelectric idea||Static Electric Materials||USA|
|What do the signs mean||Force Between Two Objects||Australia|
|Difference in echo times||Sound Echoes||Tanzania|
|Electricity for water heater||AC Wiring||USA|
|Questions on electromagetism||Basics of Magnetism||India|
|Noise comes on every day||Noise Reduciton||UK|
|How do electromagnets work in railway signals?||Electromagnetic Devices||India|
|How does pressure affect a liquid?||Pressure||Ghana|
|Placing electromagnet inside another electromagnet||Electromagnets||USA|
|Advantage or application of friction||Friction||Nigeria|
|Need to update home voltages||AC Wiring||USA|
Equation different in textbook
March 2, 2017
In textbook eq. is given in terms of v, but in your lesson its given in terms of lambda.
Rajendra prasad - India (27919)
The velocity of a waveform--especially for light or sound--is often designated as "c" instead of "v". Lambda represents the wavelength.
You can also rearrange the equation to be wavelength = velocity/frequency.
Also see Doppler Effect Equations for Sound.
Using static electricity to charge phone
February 24, 2017
if i somehow generated this static electricity, how would i use it for turning on something ?
and how much electricity needed to make a phone charger work for example ?
nada - Egypt (27904)
Static electricity is static and does not move like DC or AC electricity.
Most phone chargers use alternating current (AC) electricity to charge the batteries. However, there are some new chargers that use the wireless electricity signals to charge the batteries.
Static electricity can be used to generate sparks. That might be able to turn something on. But also, the sparks can cause damage to electrical devices.
Uses for friction
February 23, 2017
List 12 uses of friction and disadvantages of friction
ade - Nigeria (27902)
References on electrostatic painting
February 20, 2017
I am Working on A project On High Voltage Engineering and i need any Reference talking about Electrostatic Painting
Mahmoud - Egypt (27892)
Some websites explaining the basics of electrostatic painting are:
Electrostatic Spray Painting Basics Explained
How Does Electrostatic Spraying Work?
I hope that helps. Best wishes for success in your project.
New Triboelectric idea
February 20, 2017
Good Day to you sir,I have taken an interest on your webpage because I also work on Triboelectric generation techniques of my own that are considered totally outside of the box thinking. If you would be interested, I would very much like a moment of your time. THANK YOU
Benjamin - USA (27893)
It is good that you are coming up with some new applications.
I'm not sure if I could help you, but I'd be glad to take a look at your idea.
What do the signs mean
February 19, 2017
Hey I'm Aric and I'm trying to work out the gravitational attraction between the Sun and the Earth for homework
I just wanna know what the times, divide, plus and minus mean
Like as in;
* = Times?
/ = Divide/Fraction
- = Minus
and so on
Aric - Australia (27888)
The equation F = GMm/R^2 means G times M times m divided by R squared or R times R.
To answer your question:
a*b means a times b or multiply a times b
a/b is a divided by b
a - b is a minus b or subtract b from a
The big thing is to find the mass of the Sun and of the Earth, as well as the distance between them.
I hope that helps. Best wishes in getting the problem solved.
Difference in echo times
February 19, 2017
a helcopter is hovering at an altitude of 200 m above the surface of a lake. a speaker on the helcopter is sending out soundwaves,which are reflected from both the surface of the water and the bottom of the lake. if the difference in arrive times of the two echoes is measured tobe 0.24s, what is the depth of the lake?
(the atmopheric temperature is 20centgreds)
Toroma - Tanzania (27890)
Most of the sound would be reflected at the surface of the water. Only a very small amount of the sound would go into the water. Also much of the sound would be reflected at the surface when trying to go back into air. In other words, the amount of sound reflected off the bottom of the lake probably could not even be detected.
The speed of sound in air is 343 m/s. So, it would take 200/343 = 0.58 seconds for the sound to go from the water to the helicopter.
The speed of sound in water is 1484 m/s. The sound would have to go to the bottom of the lake and then back up, and then it would take 0.58 s to reach the helicopter. For the difference to be 0.24 s, the depth would be 1/2 of 1484 * 0.24 = 178.08 m.
I hope that helps.
Electricity for water heater
February 19, 2017
I just found that I have current in the system from the hot wire of the water heater to ground . On one 110 with it removed from the breaker I get a reading of 1.7 volts to ground. The other reads .8 volts to ground. We went to checking because the power bill has been high and though that the water heater might have gone back. This is a older home and has had several changes over years. What would be the best way to find out what is going on.
Thanks for you help
Ben - USA (27891)
Often older homes have their electrical wiring installed or fixed incorrectly. I'm not sure how you could get readings of only 1.7 volts unless you have your voltmeter set wrong or the voltages are not for heating the water.
Although you probably hate to spend the money, it is best to get an electrician take a look at things. There may be some other reasons your power bill has been high, especially if the increase is recent.
Best wishes on solving your problem.
Questions on electromagetism
February 17, 2017
1. Ratio of Core area & Poles face area.
2. What is ATTRACTION POWER?
3. If three sides of magnet is covered with non magnetic material will there be more force on pole faces.
4. Construction & operation details of
tks. rgds, Vish
Viswanatan - India (27886)
See our lessons on Electromagnetism. They should help answer some of your questions.
Noise comes on every day
February 16, 2017
Dear Sir, please can you help me with this.
I have a building site across the road from my house.
I arrived home one day to a sound which was like my washing machine emptying out.
Since then the sound has changed. The Council monitored low voltage sound waves in the house and a sound consultant monitored 40 to 60 hertz.
Could it be that instead of hearing something emptying I actually heard something being connected to my pipes.
The sound now changes at the same time every day and I get brief interference on my TV at this time.
My main problem is that it gives me headaches and hurts my ears.
Could this be from a drainage/sump pump? Please can you give me some advice. Thank you.
Ann - UK (27884)
I am sure such a noise would be annoying to you. If they are building something across the street from your house, it could be that they are turning on some equipment at the same time each day. They fact that your TV has brief interference points to some electrical switching on or off.
It would be worthwhile to go to the building site and ask if they turn on some equipment at that certain time. This could give you a clue as to the cause of the noise.
It is possible that they have something connected to water or sewage pipes that reach your house. It could be some vibration from equipment pressing against the pipes or even pumping or draining from the pipes.
You might have to ask a few people there, and hopefully someone will give you a clue as the the cause of the noise.
I hope that helps in solving your problem. Best wishes for getting rid of that noise.
How do electromagnets work in railway signals?
February 14, 2017
How electromagnet works in railway signals?
Harsh - India (27879)
Railway signals can be flashing lights or a moving barrier.
An electromagnet could be used as a solenoid to turn on or turn off the railway signals.
The barrier is usually moved by an electric motor.
How does pressure affect a liquid?
February 6, 2017
Give 3 ways on how pressure acts on liquid
Adu - Ghana (27860)
Pressure acts on a liquid in all directions. Pressure can also increase the temperature. Pressure only decreases the volume a small amount, if at all. Likewise, the temperature that the liquid changes to a solid is only slightly affected by pressure.
Placing electromagnet inside another electromagnet
February 5, 2017
I have a new found curiosity for electromagnets. I'm not a scientist or even a student... just curious. What would happen if your electromagnet core contained another electromagnet?
Ron - USA (27857)
If the core is movable, you would have a solenoid of sorts. (See Solenoids are Electromagnetic Devices).
Instead of having a movable iron core or magnet core, you would place an electromagnet there. This would allow movement of the core to be finely tuned. However, I don't think I've even seen such a configuration.
Advantage or application of friction
February 1, 2017
advantage or application of friction
ameh - Nigeria (27852)
See Uses of Friction for some examples and uses.
Need to update home voltages
January 30, 2017
On your page AC Wiring I encourage you to change all instances of "110" to "120" when referring to household voltage, since it is set (in the US) to 170 Vp, which ends up being approximately 120 VACrms.
Noji - USA (27841)
Thanks for pointing that out. Although 110 VAC is often used, the actual average between 110 and 120 is 117 VAC. But 120 is more commonly used. I changed the pages on AC from 110 VAC to 120 VAC.
I also updated the higher voltage from 220 to 240 VAC.
Questions and comments
Do you have any questions, comments, or opinions on this subject? If so, send an email with your feedback. I will try to get back to you as soon as possible.
Click on a button to bookmark or share this page through Twitter, Facebook, email, or other services:
Students and researchers
The Web address of this page is:
Please include it as a link on your website or as a reference in your report, document, or thesis.
Where are you now?