Solving Q3 of AND and OR Circuits Challenge

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In summary, to add a buzzer to a circuit with a start-stop switch and a motor that only runs when the lid is closed, the buzzer should be placed in parallel with the lid switch. This will allow the buzzer to sound if the lid is open and the start-stop switch is operated, as the voltage across the buzzer will be zero when the lid switch is closed and the motor is running.
  • #1
smo2012
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I can't answer Q3 of:

A spin-drier has a start-stop switch, but the motor will only spin the drum if the lid is closed. Closing the lid closes an SPST switch inside the machine, and the motor can then be started with the start-stop switch.

2) Draw a diagram of a simple circuit for this (done - with battery, SPST, push switch and motor in series)

3) Add a buzzer to your circuit diagram so that the buzzer will sound if the lid is not closed and the start-stop switch is operated (remember that a buzzer requires much less current than a motor does).

I cannot work out Q3. If I add a cell and buzzer in parallel with the push switch it would sound when the lid is open and when the lid is closed so this wouldn't work.

Any help would be much appreciated!
 
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  • #2
Hi there
welcome to PF :smile:

Is this homework ??
looks much like it

How about starting with telling us what you can figure out
have you attempted to draw the circuit ? ... show us so we can then guide you

cheers
Dave
 
  • #3
I can't draw it on these forums can I? I am a first year teacher who hasn't done physics for 16 years. I want to go through this with my class tomorrow. If you could guide me then I will be able to understand it. Thanks.
 
  • #4
I cannot work out Q3. If I add a cell and buzzer in parallel with the push switch it would sound when the lid is open and when the lid is closed so this wouldn't work.

Hint: What is the voltage across the lid push button when the lid push button is open/closed.
 
  • #5
smo2012 said:
I can't draw it on these forums can I?

No, but you can draw it elsewhere and either attach the image to your post, or host it on the web and just link to the image (preferably using [noparse][/noparse] tags, so that the image is displayed as part of the post).
 
  • #6
Ok, I'm afraid I don't have time to draw and attach/scan - it's already evening here (Kenya), my work day is over and my elementary scholarship class starts at 7am tomorrow. I'd really like to do it with them if I can get an answer to this question tonight.

Watters - the voltage will be nil when the switch is open and something when the switch is closed. How does this relate? I assume that if I add the buzzer with a separate battery in parallel with the push switch, some current will still flow around the parallel circuit when the large switch is on, so this wouldn't work.
 
  • #7
Watters - the voltage will be nil when the switch is open and something when the switch is closed

That's not correct.

With the main ON/OFF switch ON and the lid switch is OPEN (=off) the voltage across the lid switch will be the battery voltage. When the switch is closed the voltage will be zero because the switch is a short circuit.

There is another hint in the problem..

(remember that a buzzer requires much less current than a motor does).

You have the right idea but won't need another battery for the buzzer.
 
  • #8
Ok, thanks CWatters, so what's the solution to the problem? Obviously the buzzer won't sound with the lid switch open as it is a series circuit, if I am right.

Thanks,
Sarah
 
  • #9
Just put the buzzer in parallel with the lid switch...

With the main switch ON and the lid open current flows from the power supply, through the ON/Off switch, through the buzzer and then through the motor back to the battery. Not enough current will flow to turn the motor because the buzzer draws little power (meaning it has quite a high resistance. Most of the supply voltage appears across the buzzer and very little across the motor. For more detail google "Potential Divider circuit"). The buzzer sounds.

With the main switch ON and the lid shut current flows from the power supply, through the ON/OFF switch, through the lid switch, through the motor (causing the motor to run) and back to the battery. The buzzer does not sound because the voltage across it is zero (It is shorted out by the lid switch).
 

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  • #10
Ah ok makes sense. Thanks a lot for your reply.
 

1. How do I solve Q3 of AND and OR Circuits Challenge?

To solve Q3 of the AND and OR Circuits Challenge, first identify the input values for each gate. Then, use the truth tables for AND and OR gates to determine the output values. Finally, compare the output values to the desired result as given in the challenge.

2. Can I use any other method to solve Q3 of AND and OR Circuits Challenge?

Yes, there are other methods that can be used to solve Q3 of the AND and OR Circuits Challenge, such as using Boolean algebra or creating a circuit diagram. However, using truth tables is a straightforward and efficient method for solving this type of problem.

3. What is the purpose of Q3 in the AND and OR Circuits Challenge?

The purpose of Q3 is to test your understanding of AND and OR logic gates and your ability to apply them in a real-life scenario. It also helps to familiarize you with truth tables and how to use them to solve logic gate problems.

4. What is the difference between an AND gate and an OR gate?

An AND gate produces an output of 1 only when both of its inputs are 1. In contrast, an OR gate produces an output of 1 when either or both of its inputs are 1. In other words, an AND gate requires both inputs to be 1 for the output to be 1, while an OR gate only requires at least one input to be 1 for the output to be 1.

5. What are some real-life applications of AND and OR gates?

AND and OR gates are used in many electronic devices, such as computers, calculators, and traffic lights. They are also used in programming and in creating logical statements. In everyday life, AND and OR gates are used in decision-making processes, where multiple conditions must be met or at least one condition must be met for a certain outcome to occur.

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