How to... check a multimeter fuse

After almost 14 years as a physics technician, I can't believe I only just figured this out!


The multimeters we use have a 250mA fuses, which often gets blown if the students have set the meter up on the wrong setting and the current is too high. For 14 years I've been dismantling meters to check whether a blown fuse is responsible for an experiment not working properly, but now I have the solution!

• take 2 multimeters - one set to ohms and the other, which you want to test, set to mA
• Connect the ohm meter across the mA meter
• If the ohm meter reads 1, then the fuse is blown and you still have to dismantle the meter to change it
• If the ohm meter reads 0 (or thereabouts) then the fuse is fine.

The meter on the left is set to ohms and is testing the one on the right. This multimeter is fine.

Adapting dynamics trollies

Your basic dynamics trolley looks something like this:

We mainly use them for experiments on velocity or acceleration and generally use a light gate for the measurements. In order to break the light beam you have to attach some sort of 'sail' to the back of the trolley which up until now has generally been a piece of cardboard stuck on with sellotape or blu tack.

That was never really an ideal way to do it. For starters it looks a mess, and the sails are often not stiff enough and will bend or fold over and not break the beam as cleanly as we want. I've been trying to come up with a solution to this problem for ages and it suddenly struck me a couple of weeks ago.

I had a load of these clips in a drawer which I didn't really have a use for. I think they're for holding pipes or cables. My thinking was, if I attach the clips to the back of the trolley then they could hold and support the sail. Even better, I had some 10cm squares of hardboard which we used for an old ISA which I thought would make ideal sturdy sails.

Initially I just glued the clips to the trollies to see if the concept was sound, and the teachers loved it! I've now screwed the clips on and hopefully our velocity practicals will be a bit smoother now.

The finished article

ps. It's now half way through lesson 1 on tuesday. Still no requisition sheet from astroboy!

Gold Leaf Electroscope

Got my Gold Leaf Electroscopes out this morning, ready for a lesson, only to discover that 4 of them have no gold leaf. Not a problem - I quite like fitting new gold leaf. It's a bit fiddly but not difficult.

Here is my 'how to' guide to fitting gold leaf.

Disclaimer - this is not the only way, probably not even the best way. It's just my way.

Remove any traces of old gold leaf or adhesive from the stem of the electroscope and clean off any grease with a little ethanol.

With the gold leaf (actually it's an alloy called dutch metal) between 2 thin pieces of paper, cut a strip 40mm by 5mm.

Cut a thin strip of sellotape and stick it to the top end of the gold leaf  then carefully position onto the stem. Reassemble electroscope and admire your handywork!

There's a guide here on the lovely TechKnow website which shows a different way to attach the gold leaf, using spit. I've not tried it, but it may be worth a try!