Need help preparing for the MCAT physics section? MedSchoolCoach expert, Ken Tao, will teach you what you need to know about power, ammeters, and voltmeters in circuits. Watch this video to learn how to do well on the physics section of the MCAT exam!
Power is defined as the rate at which work is done, measured in units of watts (W). Looking at circuits, power can also be defined as the rate at which electrical energy is transferred. For instance, we could measure the rate at which the battery is delivering power to the circuit, or the rate at which a resistor is dissipating electrical energy to power a light bulb. The primary equation for power is current times voltage, but we can use Ohm’s law to rearrange this into several other equations for power, shown below. What is useful about this is that if the MCAT provides you with any two of voltage, current, and resistance, we can calculate power.
Ammeters and Voltmeters
Meters are devices that are used to measure different values within a circuit. Ammeters are used to measure current, by connecting the ammeter in series to the circuit element you want to measure the current for. An ammeter should have minimal resistance, in order to not disturb the circuit. Voltmeters are used to measure voltage, by connecting the voltmeter in parallel to the circuit element whose voltage you want to measure. When you have circuit elements in parallel, current has two different paths that it can flow through. Since we want the meter that we're using to affect the circuit as little as possible, we want all the current to pass through the resistor and not the voltmeter. If we pick a voltmeter with extremely high resistance, then all the current will just go through the circuit element whose current you're trying to measure, minimizing its effect on the circuit. In summary, a good ammeter should have low resistance and be connected in series, while a good voltmeter should have high resistance and be connected in parallel.
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7 сен 2024
