Ohm's Law Problems: Solving for Resistance and Current

In summary, Ohm's law states that the current in a circuit is directly proportional to the voltage and inversely proportional to the resistance. An ideal ammeter has no resistance and measures the current without changing it, while an ideal voltmeter has an infinite resistance and measures the voltage difference without changing it. Voltmeters are connected in parallel and ammeters are connected in series. Using Ohm's law, the potential difference across a 220-Ω resistor can be found by multiplying the resistance by the current. The resistance of a 40-W electric lamp can be found using the formula for power and the given information. The operating resistance of a three-cell flashlight can be found by using the sum of the individual voltages
  • #1
nutzweb
12
0
ohm's law problems. help...

Research Work:

What is an ideal ammeter and an ideal voltmeter? Why are voltmeters connected in parallel? Why are ammeters connected in series?

Problems:

answer any number that you know. thanks so much. i just neede it badly...

1.What is the potential difference across a 220-Ω resistor when a current of 3.50 A flows through it?

2.A 40-W electric lamp draws a current of 0.33 A when operated with a potential difference of 120 V. What is the resistance of the lamp?

3.A three-cell flashlight draws a current of 0.60 A. What is the operating resistance of the light bulb if each cell provides a potential of 1.0 V when delivering this current?

4.The current through an electronic device is measured for several different voltages applied across the device. When the potential difference is 0 V, 0.50 V, and 0.75 V, the current is 0 A, 0.010 A, and 0.015 A, respectively. Does the device obey Ohm’s Law?
 
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  • #2
An ideal ammeter would be one that could measure the current in a circuit without changing it. It would have no resistance. An ideal voltmeter would be one that could measure the voltage difference between two points in a circuit without changing that voltage. It would have an infinite resistance.

Voltmeters measure the votage difference between two points in a circuit. If you connrcted one in series with a circuit, think about what you would be measuring. That should explain why they are generally connected in parallel.

Ammeters measure the current flowing through them and have very little resistance. Think about what would happen if you connected one in parallel. Since it would alter the current flowing in the rest of the circuit, what you would be measuring wouldn't be very meaningful.

1. Try Ohm's law: V=IR
2. Use the formula for the power, P, to solve for R: [itex]P=I^2R[/tex] (The problem gives extra information, but is not inconsistant with itself.)
3. Presumably the cells are connected in parallel and the total voltage is the sum of the ndividual voltages. From there it's just Ohm's law again.
4. Basically, just solve for R in Ohm's law for each voltage (other than 0, as this will be indeterminant). Is R the same in each case?
 
  • #3
1/ V= 220*3.50 =770
2/ R = 120/0.33 =363.6
3/ R = (1+1+1)/0.6 =5
4/ V= 0*R, V=0.5=0.010*R => R =50, V=0.75=0.015*R => R=50 So YES.
 

1. What is Ohm's law?

Ohm's law is a fundamental law in physics that describes the relationship between voltage, current, and resistance in an electrical circuit. It states that the current flowing through a conductor is directly proportional to the voltage and inversely proportional to the resistance.

2. How do I use Ohm's law to solve problems?

To solve problems using Ohm's law, you need to know the values of two of the variables (voltage, current, or resistance) and use the formula V=IR to calculate the value of the third variable. It is important to use consistent units for all values (e.g. volts, amps, and ohms).

3. Can Ohm's law be applied to all electrical circuits?

Yes, Ohm's law can be applied to all electrical circuits, as long as the circuit is made up of linear components (such as resistors) and the temperature remains constant. Non-linear components, such as diodes and transistors, do not follow Ohm's law.

4. What is the difference between series and parallel circuits in terms of Ohm's law?

In series circuits, the total resistance is equal to the sum of individual resistances, so Ohm's law can be applied to the entire circuit. In parallel circuits, the total resistance is less than the smallest individual resistance, so the current is divided between the branches and Ohm's law cannot be applied to the entire circuit.

5. How can I check if my calculations using Ohm's law are correct?

You can use a multimeter to measure the voltage and current in the circuit and compare them to the values you calculated using Ohm's law. If they are close, then your calculations are likely correct. You can also use Kirchhoff's laws to check the accuracy of your calculations.

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