SHAP - STA
Binary star model
Eclipsing binary stars
Two stars orbiting each other so that the stars pass in front of each other when viewed
from the earth are called eclipsing binary stars. You are going to use the model of an
eclipsing binary star to see how to calculate the mass of a star in an eclipsing binary
system.
Apparatus:
Binary star model
Power pack
Light sensor
Datalogger
Lead for light sensor
2 Retort stands and clamps
Set up the binary star model in a retort stand and clamp so that the two balls turn in the
horizontal plane.
Attach a power pack to the motor and adjust the supply to turn the motor slowly (use a
supply of less than 2 V d.c.).
Use another retort stand to hold the light sensor level with the stars about 1 metre away
from the model.
Plug the sensor into the datalogger. Change the sampling rate to 50 samples/second.
Turn on the lights on the model and the motor.
Start the datalogger for a couple of rotations of the model and then stop the datalogger
and rescale the graph to observe the shape.
1. Sketch the shape of the graph and label it to explain what is happening at
significant points.
2. Measure the period of rotation.
The scale of the model is:
1 second on the model is 1 year in real life
1mm on the model is 1x1010m in real life
3. Calculate the mass of the stars.
Change the rotation period and try the questions again.
David Swinscoe & Chris Pambou
City and Islington Sixth Form College
1
Construction of the binary stars model
Materials
Economy gearbox and motor
Battery box (2 x AA with switch)
AA batteries
MES lamp holder
MES bulb 2.5V/0.2A
Resistor
Table tennis balls
Plastic gear
CD/DVD
Rapid
“
“
“
“
local purchase
37-0165
18-2906
18-4210
41-0070
41-0782
£2.85
£0.42
£0.29
£0.25
£0.06
x1
x1
x2
x2
x2
£0.10
x2
x1
x1
Construction
Using a glue gun attach the two MES lamp holders to the CD/DVD approximately 2cm apart.
To the underside of the CD/DVD glue the plastic gear centrally to act as the spindle support and
then glue the battery box.
Wire the battery box to the first lamp holder and then connect the second bulb holder in parallel
with a 2.2Ω resistor.
Insert bulbs and batteries. Carefully cut a small cylindrical hole on each table tennis ball and attach
to the bulb holders (you may need a small ball of glue to hold them).
Insert the gearbox spindle to the gear and attach the whole assembly using a clamp and stand.
David Swinscoe & Chris Pambou
City and Islington Sixth Form College
2