How do you figure out what resistors to use?
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How do you figure out what resistors to use?
Determine the voltage and current needed for your LED. We’ll use the following formula to determine the resistor value: Resistor = (Battery Voltage – LED voltage) / desired LED current. For a typical white LED that requires 10mA, powered by 12V the values are: (12-3.4)/. 010=860 ohms.
How can you combine three resistors of 9 Ohm each to get a resistance of 12 ohm?
It is not possible to have a 12 ohm resistance with three 9 ohm resistances in any combination.
- If we connect 2 resistances of 9 ohms in parallel, their combination will give 9/2 = 4.5 ohm.
- If all the resistances are connected in series, we get total resistance of 27 ohms.
Can you combine resistors?
Resistors in series can simply be “added up.” For example, the diagram to the left shows an original circuit with three resistors: A, B, and C. If you wanted to combine these, the equivalent resistor would simply be A+B+C ohms.
How would you connect 3 resistors each of 9 ohms to get the equivalent resistance as a 6 ohms B 13.5 ohms?
- R=9/2=4.5Ω
- R’=R+R3
- =4.5+9=13.5Ω
- (ii) Two resistors in series and one in Parallel.
- R=R1+R2=9+9=18Ω
- 1/R’=1/R+1/R0=1/18+1/9=1+2/18=3/18.
- R’=18/3=6Ω
How would you connect three resistors each of Resistance 6 Ohm?
Answer: To obtain a combined resistance of 9 ohms, three resistors each of resistance 6 ohm should be connected in a parallel circuit and one in series. In a parallel circuit, the equivalent resistance of all the resistors connected is equal to the reciprocal value of the sum of the individual resistances.
Why do we use two 100K ohm resistors in series instead of 200K resistor?
Two 100K resistors in series will give you a value of 200K. The differences are: Total heat dissipation is the same but now spread over a larger area. This is only an issue if you have temperature sensitive components nearby.