Practical Measuring EMF / b Fueld Using A Search Coil Flashcards
What is a search coil with oscilloscope and why do we use it
Search coil is a device with some turns that basically due to a changing magnetic field in the solenoid produces an emf in the turns which is picked up. Y the oscilloscope
Thus it allows us to measure the emf and can use this for experiments comparing it the theta, area etc
We use a search coil to measure ac because more accurate than a ac voltmeter as the emf lroduced is already very low
How could a search coil measure b field in a solenoid
Search coil oscillate strictly measures emf produced, in the search coil, however provided the number of turns, area, FREQUENCY (due to omega, keep the ac current frewuency CONSTANT) and angle of the search coil is not changed, then the emf produced will be proprtionsl to the B field received by the search coil, due to the solenoid
You can thus see how b field in the solenoid changes due to the length of solenoid or the number of turns, vary these amd ,easier the “B field” by measuring the voltage
Why must keep frewuency of ac voltsge CONSTSNT if tryna measure the b field in solenoid
How to ACHIEVE THIS?
This because we said emf prop to b field in solenoid, and emf depends on area, N, theta AND THE FREWUENCY I’m the search coil, so as long as frewuency kept constant , so the ac current, then the only things that affect the emf is the b field form solenoid
We need to keep the current constant anyways
How to measure rhe emf ? What can we do this time
As we dint care about the time ar all, can just TURN OFF TIMEBASE
Measure peak to peak emf as normal and then divide by 2 for most accuracy
What to remember to say about how many readings to take?
Always mention take 6-7 readings so a graph can be plotted
What are some thints you must ENSURE so that the practical is valid for measuring B!
(3)
For B, as we aren’t doing anything to the search coil, must make sure ti remains VERTICAL AT ALL TIMES AND COAXIAL WITH THE SLINKY
- also make sure the slinky is uniformly spaced so that NO WIRES TOUCHING EACH OTHER
- also make sure the point where Coro Ilse clips touch the slinky is only at One POINT
If changing the angle of the search coil what could be a reason for why the graoh doesn’t end up showing straight line (2)’
This could be because when you try make it perpendicular, it will never actually be really perpendicular
Also the angle you measure could be a paradox error
How to make parallax error to measure angle with protractor?
Add a little card to help measure
Where would uncertainties be
Measuring emf, if twke mean find the ucnertiwnkty in range, if not then resolution of v /v, divide by the peak to peak
- uncertainty
How to vary the number of coils or length for the measuring B one?
Change the number of coils by compressing, make sure length the same snd put corocildie clips on again
For length, keep the turns CONSTSNT and increase the length with corocilie clips
What should you do at the START of the experiment before you even begin ss a test
Do rough test to see if you get a decent voltsge range? And thus fix the frewuency and current accordingly?
Finally how to increase the sensitivity, because we already have small B and V coming out, how ti icnrease this?
Reduce or increase the other FIXED VARIABLE and this way your B values will be generally bigger so less uncertainties and potential less problems about sensitivity
