# Finding current in an electric circuit

• ImpCat
In summary, a voltmeter with a resistance of 50kΩ was used to measure the electric potential difference in a circuit with a cell of 5.0 V electromotive force and negligible internal resistance. However, the voltmeter's internal resistance was not accounted for in the initial calculation, leading to a discrepancy in the answer. By factoring in the 50kΩ resistance, the correct answer of 1 V can be obtained. It should be noted that while voltmeters are typically designed with high resistance to minimize changes in the circuit, they may not always have an infinite resistance.
ImpCat

## Homework Statement

A voltmeter of resistance 50kΩ is used to measure the electric potential difference in a circuit, as shown. The cell has an electromotive force (emf) of 5.0 V and negligible internal resistance.

I=V/R
V=IR

## The Attempt at a Solution

I=5/150000 I=3.33E-5
V=50000*3.33E-5=1.7 V

But the answer is 1 V. How?
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You did not account for the internal resistance of the voltmeter.

ImpCat
Doc Al said:
You did not account for the internal resistance of the voltmeter.

How do you account for the internal resistance of a voltmeter though? It's not provided. Plus isn't voltmeters purposefully created with high resistance so as to create as little change in the circuit as possible?

ImpCat said:
How do you account for the internal resistance of a voltmeter though? It's not provided. Plus isn't voltmeters purposefully created with high resistance so as to create as little change in the circuit as possible?
You're told it is 50kΩ. (That's separate to the resistor of the same value in the circuit.)

There may be reasons it can't always designed to be near "infinity".

ImpCat
NascentOxygen said:
You're told it is 50kΩ.

There may be reasons it can't always designed to be "infinity".

Ohhhh I see, I thought the 50kΩ is the resistance of the resistor! Maybe I should've read the question more clearly.

See my amended reply.

ImpCat

## 1. How do you calculate the current in an electric circuit?

To calculate the current in an electric circuit, you need to use Ohm's Law which states that current (I) is equal to the voltage (V) divided by the resistance (R). This can be represented by the equation I = V/R.

## 2. What is the unit of measurement for electric current?

The unit of measurement for electric current is the ampere (A), which is defined as the flow of one coulomb of charge per second.

## 3. How does the number of components in a circuit affect the current?

The number of components in a circuit does not affect the current, as long as the circuit is in series. In a series circuit, the current is the same at all points. However, in a parallel circuit, the current is divided among the branches based on the resistance of each branch.

## 4. What is the difference between AC and DC current?

AC (alternating current) and DC (direct current) are two types of current that flow through electric circuits. AC current changes direction periodically, while DC current only flows in one direction. Most household appliances and electronics use AC current, while batteries and portable devices use DC current.

## 5. How does resistance affect the current in a circuit?

Resistance is a measure of how difficult it is for current to flow through a circuit. The higher the resistance, the lower the current will be, and vice versa. This is because resistance decreases the flow of electrons, thus reducing the amount of current in the circuit.

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