SfC Home > Physical Science >

Reader questions and feedback on physical science. Also refer to physics, chemistry, astronomy, electricity, magnetism, electromagnet, light, sound, waves, forces, work, energy, friction, heat, thermodynamics, Ron Kurtus, School for Champions. Copyright © Restrictions

Answers to Readers' Questions on Physical Science:

DC

The following 83 comments and questions have been sent in. They are listed according to date.

List of first 10 items

• Can you get a shock from DC electricity?
• What happens when you recharge a battery?
• Does a solenoid become a magnet?
• How do you step up DC voltage?
• Renewable sources for electricity
• How to create DC electricity?
• Why don't we get shocked by DC electricity?
• AC versus DC in magnitude of the shock
• Why do they still use the incorrect Franklin convention?
• How is AC voltage measured?

Next 10

Can you get a shock from DC electricity?

Question

October 11, 2009

do we get any electric shock by holding dc current wire
is there any danger if doing so?

naresh - India

18476

Answer

Most DC electricity we experience comes from low voltage batteries. However, a 100 volt battery or a high voltage from a DC generator can not only give you a shock, but can also kill you.

A problem with a DC shock is that you cannot let go of the wire. With an AC shock, you let go right away.

Back to top

What happens when you recharge a battery?

Question

June 7, 2009

When charging a DC battery, are you replacing the amps or the voltage in the battery or both? Also are the amp ratings accurate for a battery or can they be higher or lower then specified?

Dennis - USA

17871

Answer

Charging a DC battery is somewhat complex.

When charging a rechargeable battery, you are causing an electrochemical reaction. One material in the battery is oxidized, producing electrons. The other material is reduced, creating positive ions. In between the terminals is an electrolyte, which acts as a buffer for the moving electrons or alliance between the terminals. So in essence you are performing a chemical action that is restoring the number of electrons in the battery.

The voltage of the battery is determined by the internal size and structure of the battery. It is the potential difference between the two terminals. This is typically a fixed number, while the amperage is determined by the amount of resistance in the circuit, according to the equation V = IR. Amps concerns the number of electrons that are flowing through the wire, so a given battery has only a certain possible supply or amperage.

Back to top

Does a solenoid become a magnet?

Question

April 29, 2009

when we provide a d.c supply to a solenoid does it become a magnet? if yes, please explain how?

raja - India

17673

Answer

When direct current passes through a wire, there is a magnetic field around the wire. Looping the wire in the form of a solenoid increases and directs the magnetic field, such that it would have north and south poles at the ends of the solenoid. Adding an iron core to the solenoid turns it into an electromagnet.

See our lesson of electromagnets at:
http://www.school-for-champions.com/science/electromagnetism.htm

Back to top

How do you step up DC voltage?

Question

March 20, 2009

How do you step DC voltage up and down

John - USA

17481

Answer

A DC to DC step-up converter can do the trick. You can purchase them in many electronics stores. For an article, with a circuit diagram, see:

http://www.rowan.sensation.net.au/electronics/stepup.html

Back to top

Renewable sources for electricity

Question

February 17, 2009

ok, one way to generate electricity is from lemon with the help of copper wires and can u please suggest me more ways to produce electricity from renewable sources like the example you have given.

ankita - India

17290

Answer

The lemon example is the basis of a common battery. Fuel cells that use hydrogen is another type of battery. Silicon wafers can create electricity from solar energy. Other sources of generation of electricity are hydroelectric generators and wind generators.

Back to top

How to create DC electricity?

Question

November 1, 2008

How to create dc current and materials needed

Mbachu - Nigeria

16718

Answer

You can create DC electricity by making a battery. A very simple one is using a lemon and copper and zinc coated wires. But it only creates 1 volt. You can also use a DC electric motor and spin the motor by hand. the output should be DC electricity.

Back to top

Why don't we get shocked by DC electricity?

Question

September 13, 2008

when we touch dc supply we will not get shock why?

raja - India

16492

Answer

Usually, the voltage is too low to get a shock. Also, you must touch both terminals to complete a circuit for the shock.

If you would touch both terminals of a 100V dry cell battery, you will certainly feel the shock.

Back to top

AC versus DC in magnitude of the shock

Question

August 23, 2008

why does we get shock due to magnitude of alternating current than the dc source with the same magnitude

raja - India

16390

Answer

A shock from AC allows you to let go of the wire, but DC does not, so in such cases DC at the same voltage is more dangerous.

But if the current goes through the heart, AC is more dangerous because the alternating current causes the heart to stop at lower current than with DC.

Back to top

Why do they still use the incorrect Franklin convention?

Question

March 3, 2008

why do they still use the incorrect Franklin convention as to the correct flow of electrons, seeing that it is in correct? Is it possible that from positive to negative "feels" better than negative to positive? But I use a rule of thumb and that is we are always taught that when we feel negative to think positive! From negative to positive. When the generator (A.C.) in an auto kicks in, it actually sends current through the battery in the opposite direction. Does this also mean that current comming normally from the battery on a circuit would now move in the opposite direction when A.C. generator kicks in? Thank you.

Larry - USA

15475

Answer

There are a number of conventions that are unscientific or misleading and should have been changed years ago. I guess it is too late now.

The generator or alternator in an automobile includes a rectifier circuit to change the AC to DC, in order to charge the battery, as well as to provide DC to the starter motor. The electrons move toward the positive battery terminal, but the designation of the current is in the opposite direction.

Back to top

How is AC voltage measured?

Question

October 25, 2007

How is Ac voltage and current measured

- USA

14637

Answer

Usually a Multimeter is used that measures AC and DC voltage, current and resistance with its different settings.

An AC voltmeter can also do the job.

Back to top

Next 10

Summary

Hopefully, this reader feedback has helped provide information about Science issues.

Resources

The following are some resources on this topic.

Websites

Science Resources

Books

Top-rated books on Physical Science

Miscellaneous

What do you think?

Do you have any questions, comments, or opinions on this subject? If so, send an email with your feedback. We will try to get back to you as soon as possible.

Feel free to establish a link from your website to pages in this site.

Where can you go from here?

School for Champions

Physical Science Topics

Answers to Readers' Questions