lab17--4/30 (RC circuits and Oscilloscope)

Activity: Capacitors, batteries, and bulbs

a.Connect a rounded #14 bulb in series with the 0.47F capacitor, a switch, and the 4.5V battery. Describe what happens when you close the circuit

 

series built up

 

b. can you  make bulb light again without battery in the circuit?

built up then dim

 

c. Draw a sketch of the approximate brightness of the bulb as a function of time when it is placed across a charged capacitor without the battery present. let t=0 when the bulb is first places in the circuit with the charged capacitor.

 

e. what happens when more capacitors is put in the circuit? when more resistance is put in the circuit?

capacitance take longer for time to charge in parallel

increased capacitors take longer time to charge

 

Quantitative measurements on an RC system

Activity: The decrease of voltage in an RC circuit

 

material: battery, capacitor, resistor, logger pro, multimeter

 

a)Record the measured V across capacitor at least every one or two seconds until the V is about 1/100th of its initial value.

 

b)Then we flip the terminal from a battery terminal to a terminal of capacitor. Record the V vs Time until V is about 1/100th of its initial value.

 

We fit exponential equation to the curve and it is perfectly fit.

 

V=V0*e^(-1/RC)

 

graph a

 

 

graph b

This is how the graph (theoretical RC decay curve) should look like:

 

 

 

 

Prof Mason did an experiment in which we saw the bulb explodes

 

 

 

Find the units of A, B

They are both in volts

 unit of c is 1/t, s^-1

 

 

Derive C and its unit

Calculate problem in RC ciucuit

Summary:
for discharge , we use V(t)=V0*e^(-t/tao)
for charging, we use V(t)=V0(1-e^(-t/tao)