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Answers to Readers' Questions on Physical Science:

AC

The following 168 comments and questions have been sent in. They are listed according to date.

List of first 10 items

• Why not use AC in a computer?
• How does radio transmission get into my radio?
• Why not use 220 V?
• Why is current greater than voltage in AC?
• Why do we need to convert AC to DC?
• Why is DC preferred in electronic circuits?
• Difference between current and voltage
• Which current is more dangerous?
• Resource for AP Physics students
• Where does DC come from in the home?

Next 10

Why not use AC in a computer?

Question

October 29, 2009

why not use AC current in Computer?

VIVEK - India

18589

Answer

Computer power supplies convert AC to low voltage DC, which is necessary for the sensitive computer components. One problem with AC is that it can create undesirable currents in a nearby wire.

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How does radio transmission get into my radio?

Question

September 14, 2009

How does a radio transmission get into my radio? What are radio waves and how do they work?

Philip - USA

18311

Answer

Radio waves area form of electromagnetic radiation that can travel long distances. When they hit the antenna in a radio, they are converted into a very low power AC current. The circuitry in your radio amplifies the signal and selects the ones for the radio station you are tuned into. The speaker then converts the signal into sound waves.

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Why not use 220 V?

Question

September 8, 2009

why a.c is used commonly? Why not voltage is generated in range of 220v?

Vipin - INDIA

18281

Answer

See Worldwide AC Voltages and Frequencies for information on what countries use 110 V AC and 220 V DC.

http://www.school-for-champions.com/science/ac_world_volt_freq.htm

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Why is current greater than voltage in AC?

Question

August 29, 2009

(1).why amplitude of current is more than the amplitude voltage in an alternating circuit.
(2).how can we remove unwanted magnetic field in tiwested current carrieng wires in electrical appliances.

sanjeev kumar - India

18226

Answer

The relationship between current and voltage is V = IR, where R is the resistance or impedance in an AC circuit. The amplitude of V or I depends on the scale you are using to measure them.

Quite often using several twisted wires reduces the magnetic field. Another way is to encase the wire in shielding. Usually, the magnetic field in an electrical appliance is not a problem, except for sensitive equipment.

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Why do we need to convert AC to DC?

Question

August 21, 2009

Why do we need to convert ac to dc

Jack - South Africa

18174

Answer

Just as some devices require AC to operate, some require DC to operate. One example is that a DC heater works better than an AC heater. Of course a DC motor requires DC electricity. Some types of lights will flicker with AC but not with DC.

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Why is DC preferred in electronic circuits?

Question

July 27, 2009

why we prefer dc in electronic circuits?

mohsin - Pakistan

18067

Answer

Most electronic circuits require resistors, capacitors and inductors in the circuitry. Capacitors and inductors require AC or a form of AC to operate, so tat the circuit can amplify, tune or such.

Many small electronics are powered by DC batteries, but the DC is converted to a form of AC to allow the circuits to operate.

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Difference between current and voltage

Question

July 24, 2009

hai sir/madam i want more informations about current and voltage and current and voltage waveforms what is the difference between current and voltage i am searching for this more than one year but i cannot get the correct answer please reply me very basic about current and voltage

- India, Tamilnadu

18057

Answer

Think of a water hose. The amount of water coming out of the hose is like current. Electrical current is the amount of electrons moving through the wire.

The water pressure in the hose is like voltage, which is the potential difference that causes the electrons to flow or move. Water pressure will overcome resistance, and voltage overcomes resistance in the wire.

See our lesson on the Basics of Electricity at:
http://www.school-for-champions.com/science/electricity.htm

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Which current is more dangerous?

Question

January 13, 2009

which current(AC or DC) is more dangerious and why?

jagadish - India

17093

Answer

If you get a shock from AC electricity, you will quickly let go of the wire. But if you get shocked with the same voltage of DC electricity, your muscles may tense and you cannot let go of the wire. That is why DC is considered more dangerous.

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Resource for AP Physics students

Question

December 1, 2008

Hi! I like your page - I am trying to provide some resources to my AP Physics students to compliment the textbook, and this is a nice source for that.

I have read repeatedly that there was a big fight between Edison and Tesla about this, and why Tesla's ideas are so much better, but I have never read anything about how the world worked before the world switched to AC.

Liz - USA

16873

Answer

Thanks for your feedback.

The biographies of Edison, Tesla and Westinghouse give the background of the struggle between using AC and DC. They should provide interesting reading for your students.

http://www.school-for-champions.com/biographies/edison.htm

http://www.school-for-champions.com/biographies/tesla.htm

http://www.school-for-champions.com/biographies/westinghouse.htm

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Where does DC come from in the home?

Question

November 20, 2008

I have a understanding now but still don't fully understand DC electrical current. When electricity comes to your home is it not AC electricity? If it is where does DC come from? And when I am measuring the resistance in something what does that mean I'm measuring?

Cory - Canada

16835

Answer

The electricity comes into your home as AC. Devices in your home that use DC are either powered by batteries or use an adapter, which converts AC to DC, as well as lowers the voltage.

Resistance is similar to friction against the motion of electrons in a wire. That resistance is the same for both AC and DC electricity.

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