Lab Notes: Week 4, Joule Heating and Newton's Law of Cooling, Physics 3LB at UCI

Wk 4: Joule Heating and Newton's Law of Cooling
Sunday, January 26, 2020 8:33 PM




• Rate of internal energy change(W)= mc*deltaT


○ Also equals mc ≃ mwcw + mrcr * dT/dt P = IV = V^2/R = I^2R
P = I2 R

○ w: water, r: resistor


• The electrical power P dissipated in a resistor is proportional to the voltage Temp->
Voltage

across the resistor V and the current flowing through the resistor I. Time



○ Power: rate of energy change


• Rate of heat transfer: Q = K (T - Troom)


○ T: water's temp, Troom : room temp.


• Expt setup: Monitor (computer+keyboard) -> Interface -> transducer


(thermocouple). Analogous signal from transducer is converted into digital


signal w/ monitor.


• Newton's Law of Cooling: temp decays exponentially over time.


• In this expt, we use a microcomputer as a transient digitizer and plot temp as a


function of time.


○ Transient digitizer: device that samples the voltage at regular time


intervals and stores that info.


○ Transducer converts temp (specifically changes its resistance to a


function of temp)into voltage -> PC plots said voltage.