When is the potential difference across a capacitor an emf?
Only when the current being drawn from or put into the capacitor is zero. Capacitors, like batteries, have internal resistance, so their output voltage is not an emf unless current is zero. This is difficult to measure in practice so we refer to a capacitor’s voltage rather than its emf. But the source of potential difference in a capacitor is fundamental and it is an emf.
Phet explorations: circuit construction kit (dc only)
An electronics kit in your computer! Build circuits with resistors, light bulbs, batteries, and switches. Take measurements with the realistic ammeter and voltmeter. View the circuit as a schematic diagram, or switch to a life-like view.
An
circuit is one that has both a resistor and a capacitor.
The time constant
for an
circuit is
.
When an initially uncharged (
at
) capacitor in series with a resistor is charged by a DC voltage source, the voltage rises, asymptotically approaching the emf of the voltage source; as a function of time,
Within the span of each time constant
, the voltage rises by 0.632 of the remaining value, approaching the final voltage asymptotically.
If a capacitor with an initial voltage
is discharged through a resistor starting at
, then its voltage decreases exponentially as given by
In each time constant
, the voltage falls by 0.368 of its remaining initial value, approaching zero asymptotically.
Conceptual questions
Regarding the units involved in the relationship
, verify that the units of resistance times capacitance are time, that is,
.
The
time constant in heart defibrillation is crucial to limiting the time the current flows. If the capacitance in the defibrillation unit is fixed, how would you manipulate resistance in the circuit to adjust the
constant
? Would an adjustment of the applied voltage also be needed to ensure that the current delivered has an appropriate value?
When making an ECG measurement, it is important to measure voltage variations over small time intervals. The time is limited by the
constant of the circuit—it is not possible to measure time variations shorter than
. How would you manipulate
and
in the circuit to allow the necessary measurements?
Draw two graphs of charge versus time on a capacitor. Draw one for charging an initially uncharged capacitor in series with a resistor, as in the circuit in
[link] , starting from
. Draw the other for discharging a capacitor through a resistor, as in the circuit in
[link] , starting at
, with an initial charge
. Show at least two intervals of
.
When charging a capacitor, as discussed in conjunction with
[link] , how long does it take for the voltage on the capacitor to reach emf? Is this a problem?
When discharging a capacitor, as discussed in conjunction with
[link] , how long does it take for the voltage on the capacitor to reach zero? Is this a problem?
Referring to
[link] , draw a graph of potential difference across the resistor versus time, showing at least two intervals of
. Also draw a graph of current versus time for this situation.
Questions & Answers
I'm interested in biological psychology and cognitive psychology
Communication is effective because it allows individuals to share ideas, thoughts, and information with others.
effective communication can lead to improved outcomes in various settings, including personal relationships, business environments, and educational settings. By communicating effectively, individuals can negotiate effectively, solve problems collaboratively, and work towards common goals.
it starts up serve and return practice/assessments.it helps find voice talking therapy also assessments through relaxed conversation.
miss
Every time someone flushes a toilet in the apartment building, the person begins to jumb back automatically after hearing the flush, before the water temperature changes. Identify the types of learning, if it is classical conditioning identify the NS, UCS, CS and CR. If it is operant conditioning, identify the type of consequence positive reinforcement, negative reinforcement or punishment
nature is an hereditary factor while nurture is an environmental factor which constitute an individual personality. so if an individual's parent has a deviant behavior and was also brought up in an deviant environment, observation of the behavior and the inborn trait we make the individual deviant.
Samuel
I am taking this course because I am hoping that I could somehow learn more about my chosen field of interest and due to the fact that being a PsyD really ignites my passion as an individual the more I hope to learn about developing and literally explore the complexity of my critical thinking skills
