Calculating Time to Discharge Capacitor to 3V

In summary, the problem is to determine the time it takes for a capacitor with a capacitance of 1.5E-6F and a resistance of 1E3ohms to discharge from an initial voltage of 25v to a final voltage of 3v. Using the equations T=RC and v=Vi*e^(t/T), the time constant is calculated to be 1.5E-3s. Solving for t, it is found that t = Cln(A/B). However, there seems to be confusion about whether to solve for t or use a normalised universal time constant curve to estimate time.
  • #1
Rupturez
6
0

Homework Statement


Determine how long it takes the capacitor to discharge to a value of 3v
C=1.5E-6F
R=1E3ohms
Vi=25v
Vf=3v


Homework Equations


T=RC
v=Vi*e^(t/T)



The Attempt at a Solution


T=1000*1.5E-6
T=1.5E-3s

Vf(3v) is 12% of the initial 25v

Im having trouble solving for time with this equation v=Vi*e^(t/T)

many thanks in advance
 
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  • #2
Should I be solving for t or using a normalised universal timeconstant(RC) curve to estimate time?
 
  • #3
Rupturez said:

Homework Statement


Determine how long it takes the capacitor to discharge to a value of 3v
C=1.5E-6F
R=1E3ohms
Vi=25v
Vf=3v


Homework Equations


T=RC
v=Vi*e^(t/T)



The Attempt at a Solution


T=1000*1.5E-6
T=1.5E-3s

Vf(3v) is 12% of the initial 25v

Im having trouble solving for time with this equation v=Vi*e^(t/T)

many thanks in advance

Firstly [itex] V = V_i e^{-t/T}[/itex] there's a negative sign reflecting the decay of the voltage... it doesn't grow!

Secondly solving this for t is basic algebra, apply inverse operations until you isolate t.
[itex] A = B e^{t/C}[/itex]
[itex]A/B = e^{t/C}[/itex]
[itex]\ln(A/B) = t/C[/itex]
[itex]C\ln(A/B) = t[/itex]
 
  • #4
Thanking you jambaugh
 
  • #5


I would approach this problem by using the equation T=RC, where T is the time constant, R is the resistance, and C is the capacitance. In this case, T=1000*1.5E-6=1.5E-3s. This means that it will take approximately 1.5 milliseconds for the capacitor to discharge to 1/e (approximately 37%) of its initial voltage.

To calculate the time it takes for the capacitor to discharge to 3V, we can use the equation v=Vi*e^(t/T), where v is the voltage at any given time, Vi is the initial voltage, and t is the time. In this case, we know that v=3V, Vi=25V, and T=1.5E-3s. We can rearrange the equation to solve for t, giving us t=T*ln(v/Vi)=1.5E-3*ln(3/25)≈0.00047 seconds.

It's important to note that this is an ideal calculation and may not perfectly match the actual time it takes for the capacitor to discharge in real-world conditions. Factors such as internal resistance, leakage, and fluctuations in the power source can affect the actual discharge time.
 

Related to Calculating Time to Discharge Capacitor to 3V

What is a capacitor and how does it discharge?

A capacitor is an electronic component that stores electrical energy. When a capacitor is charged, it has a positive and negative side, and there is a potential difference between the two sides. When the capacitor is connected to a circuit, it will discharge its stored energy until the potential difference between the two sides is equal.

Why is it important to calculate the time to discharge a capacitor to 3V?

Calculating the time to discharge a capacitor to 3V is important because it allows us to determine how long it will take for the capacitor to reach a safe voltage level. This is especially important in electronic circuits where a certain voltage level is required for the circuit to function properly.

What factors affect the time it takes for a capacitor to discharge to 3V?

The time it takes for a capacitor to discharge to 3V is affected by the capacitance of the capacitor, the resistance of the circuit it is connected to, and the initial voltage of the capacitor. A higher capacitance or lower resistance will result in a longer discharge time, while a higher initial voltage will result in a shorter discharge time.

How can I calculate the time it takes for a capacitor to discharge to 3V?

The time it takes for a capacitor to discharge to 3V can be calculated using the formula t = RC ln(Vi/Vf), where t is the time, R is the resistance of the circuit, C is the capacitance of the capacitor, Vi is the initial voltage, and Vf is the final voltage (in this case, 3V).

Can I speed up the discharge time of a capacitor to 3V?

Yes, there are a few ways to speed up the discharge time of a capacitor to 3V. One way is to increase the resistance of the circuit, which will result in a shorter discharge time. Another way is to decrease the capacitance of the capacitor, which will also result in a shorter discharge time. Additionally, you can discharge the capacitor through a resistor or a short-circuit to speed up the process.

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