Theoretical AC/DC Circuits: 1.5V Light Bulb & Battery

In summary, a light bulb is a resistor that glows when a current is passed through it, regardless of whether the current is DC or AC. The direction of current flow does not affect the light bulb's function. However, in everyday appliances like a flashlight, the positive and negative terminals must be positioned correctly for the device to work. This is to ensure proper connection and prevent potential hazards. Therefore, the advantage of adding cases to these appliances is to guide users in correctly placing the batteries and to prevent accidents or malfunctions.
  • #1
Red_CCF
532
0
Out of curiousity, I am wondering what happens, theoretically of course, if we place a 1.5V AC light bulb (which do not exist) onto a DC circuit with a 1.5V battery? What would happen if we connect this battery backwards on the circuit (positive to the negative terminal and vice versa). This question arises from my confusion of positive and negative voltages in AC and DC circuits.
 
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  • #2
A light bulb is just a resistor that glows.

If you put 1.5 VDC across it, it will glow steadily. If you put 1.5 VAC across it, it will glow and then darken and then glow again, at the frequency of your AC. If this frequency is high enough (60 Hz is plenty), the variation is brightness will not be perceptible.

Like a resistor, it does not matter which way you connect your light bulb to your battery. Either way, the same amount of current will flow -- just in the opposite direction. The light bulb is not sensitive to the direction of current flow, though, so you won't see any difference.

- Warren
 
  • #3
chroot said:
A light bulb is just a resistor that glows.

If you put 1.5 VDC across it, it will glow steadily. If you put 1.5 VAC across it, it will glow and then darken and then glow again, at the frequency of your AC. If this frequency is high enough (60 Hz is plenty), the variation is brightness will not be perceptible.

Like a resistor, it does not matter which way you connect your light bulb to your battery. Either way, the same amount of current will flow -- just in the opposite direction. The light bulb is not sensitive to the direction of current flow, though, so you won't see any difference.

- Warren

If a light bulb does not care which direction the current is coming from, then why must everyday appliances like a flashlight have positive and negative terminals that we must position our batteries to comply or else the device doesn't work?
 
  • #4
Try it and find out if that's really true...

[note: don't try it on an LED flashlight!]
 
  • #5
Red_CCF said:
If a light bulb does not care which direction the current is coming from, then why must everyday appliances like a flashlight have positive and negative terminals that we must position our batteries to comply or else the device doesn't work?

With a regular incandescent bulb, it doesn't matter which way you put the batteries in as long as they're both polarized correctly in relation to each other. Battery cases, however, are usually set for the negative (non-nippled) end of the battery to impinge upon a spring terminal.
 
  • #6
russ_watters said:
[note: don't try it on an LED flashlight!]
No harm in reversing the batteries, it just won't work. Diode breakdown voltage is typically >20VDC. Application of a 60Hz AC (low voltage) source to the LED will cause it flash on/off, appearing to the eye as a lower than normal intensity.
 
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  • #7
Danger said:
With a regular incandescent bulb, it doesn't matter which way you put the batteries in as long as they're both polarized correctly in relation to each other. Battery cases, however, are usually set for the negative (non-nippled) end of the battery to impinge upon a spring terminal.

Oh okay; so if the cases don't exist then I can put a battery (assuming a flashlight with only one battery) whichever way I want and the flashlight will still work?

But if what I said is true then what's the advantage of adding the cases?
 
  • #8
Red_CCF said:
But if what I said is true then what's the advantage of adding the cases?

Take a flashlight that requires two batteries.

Have the users put them in however they want.

Disconnect your technical support when case after case of unhappy customers are mad their batteries exploded on you.
 
  • #9
Red_CCF said:
Oh okay; so if the cases don't exist then I can put a battery (assuming a flashlight with only one battery) whichever way I want and the flashlight will still work?

But if what I said is true then what's the advantage of adding the cases?

Yes, it will still work. What I meant by 'case' is simply the receptacle into which the batteries are inserted. Most have one solid contact and one spring-loaded one. The positive (nipple) end of the battery contacts the solid piece, and the negative (flat) end contacts the spring. In a side-by-side arrangement, the directions are usually reversed so that one goes in backwards in reference to the other. That's the easy way to put them in series without excess wiring. Most cases these days are also marked with '+' and '-' signs in the appropriate locations.
 
  • #10
mheslep said:
No harm in reversing the batteries, it just won't work.
I know, I just didn't want to confuse the OP.
 
  • #11
Tac-Tics said:
Take a flashlight that requires two batteries.

Have the users put them in however they want.

Disconnect your technical support when case after case of unhappy customers are mad their batteries exploded on you.
Also, as was noted earlier, the terminals may or may not be mechanically interchangeable and batteries are not all exactly the same shape.
 

1. What is a theoretical AC/DC circuit?

A theoretical AC/DC circuit is a simplified representation of an electrical circuit that uses alternating current (AC) and direct current (DC) to power a light bulb. It does not take into account real-world factors such as resistance, capacitance, and inductance.

2. How does a 1.5V light bulb work in this circuit?

In a theoretical AC/DC circuit, a 1.5V light bulb works by converting the electrical energy from the battery (DC) into light energy. The flow of current through the filament of the light bulb causes it to heat up and emit light.

3. What is the purpose of using both AC and DC in this circuit?

The use of both AC and DC in this circuit allows for a more constant and stable flow of electricity. AC is used to supply the initial burst of energy to power the light bulb, while DC is used to maintain a steady flow of electricity to keep the light bulb lit.

4. Can this theoretical circuit be used in real-life applications?

No, this theoretical circuit is simply a simplified model for understanding the principles of AC and DC circuits. In real-life applications, factors such as resistance, capacitance, and inductance must be taken into account to ensure safe and efficient use of electricity.

5. What are the advantages of using a 1.5V light bulb and battery in this circuit?

One advantage is that the low voltage of 1.5V is relatively safe to handle and poses a lower risk of electrical shock. Additionally, the low power consumption of the light bulb and battery make it an energy-efficient option for simple lighting applications.

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