Calculating Time Until Voltage Falls in a Circuit with Resistor and Capacitor

AI Thread Summary
To calculate the time until the voltage across a capacitor falls to a specific fraction of its initial value, the time constant (T) is determined using the formula T = cR, where c is the capacitance and R is the resistance. For a capacitor of 35 microfarads and a resistor of 120 ohms, the time constant can be calculated, and the voltage decay can be expressed using V(final) = V(initial) e^(-t/CR). Logarithms may be necessary to solve for time when setting the voltage to the desired fraction. Additionally, in a circuit with an uncharged capacitor and a bulb, the bulb will initially remain off, then gradually light up as the capacitor charges, becoming brighter over time. This behavior is consistent with the charging process of a capacitor in a series circuit.
SMUDGY
Messages
20
Reaction score
0
--------------------------------------------------------------------------------

If a charged capacitor c=35 micro farads is connected to a resistor R=120 ohms how much time will elapse until the voltage falls to 10^6/D of its original max value?

Ciruit contains a switch, resistor, emf and a capacitor in series.

Relevant equations are Time constant= T=cR and V(Final)=V(initial) e^-t/cr


I think it requires logarithms but i am not sure.

Can you please help me how to answer this.
 
Physics news on Phys.org
Another question is:

A circuit containing a switch, Vo, a capacitor and a bulb in series.

The capacior is originally uncharged. Describe the behaviour of the bulb from the instant the switch is on until a long time later.

I think there will be a delay for the bulb to emit light and then it will emit light getting slowly brighter as the capacitor is getting charged up.

Is this right?
 

Thread 'Struggling to understand the concept of this question (ice cube in water optics question)'

TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...
View full post »
Thread 'Variable mass system : water sprayed into a moving container'

Thread 'Variable mass system : water sprayed into a moving container'

Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
View full post »

Similar threads

Calculating the voltage across capacitors and resistors with switches
Replies
2
Views
774
Finding Current in Resistors & Charge of Capacitor
Replies
4
Views
2K
Circuit with resistor, switch and capacitor
2
Replies
62
Views
5K
Energy dissipated in the resistors in a 2 mesh RC circuit
Replies
1
Views
2K
RC Circuit with parallel resistor
Replies
6
Views
3K
Calculation of current in driven series RLC circuit
Replies
8
Views
2K
Calculating Voltage Decay in a Resistor-Capacitor Circuit
Replies
1
Views
2K
How to find voltage across capacitor in RLC circuit?
Replies
3
Views
1K
Finding the time for charging Voltage
Replies
9
Views
2K
Drawing a Circuit from Voltage-Time Graph
Replies
7
Views
4K

Hot Threads

Recent Insights

Back
Top