# The Naked Scientists Forum

### Author Topic: i reaaaaally need some help here!  (Read 2536 times)

#### jezza

• Jr. Member
• Posts: 36
##### i reaaaaally need some help here!
« on: 01/06/2006 22:53:37 »
ok, electronics exam tomorrow, and I could do with some help on a few questions, some of this stuff ill Google, but some more input would be great.

1) what is the concept of a rotating phasor?

2) the DMM and CRO are both versatile measuring instruments. identify which instruments you would select in order to check the following signals, give reasons for your choice and comment on the value and accuracy of the instrument.
I) the a.c mains voltage
ii) a computer clock signal
iii) an audio CD pre amp output

3) A metal film resistor has a resistance of 200 ohms, when its mean temperature is 20'C calculate its resistance when its mean temperature is at 80'C
assume the temperature coefficient of resistance alpha(0) of the wire is 0.00428 per 'C, the following formula  may be useful: R1 = R0 (1+alpha(0)t)

that’s it, any advice what so ever would be reallllllly helpful, thanks

#### another_someone

• Guest
##### Re: i reaaaaally need some help here!
« Reply #1 on: 01/06/2006 23:18:25 »
quote:
Originally posted by jezza

ok, electronics exam tomorrow, and I could do with some help on a few questions, some of this stuff ill Google, but some more input would be great.

1) what is the concept of a rotating phasor?

2) the DMM and CRO are both versatile measuring instruments. identify which instruments you would select in order to check the following signals, give reasons for your choice and comment on the value and accuracy of the instrument.
I) the a.c mains voltage
ii) a computer clock signal
iii) an audio CD pre amp output

3) A metal film resistor has a resistance of 200 ohms, when its mean temperature is 20'C calculate its resistance when its mean temperature is at 80'C
assume the temperature coefficient of resistance alpha(0) of the wire is 0.00428 per 'C, the following formula  may be useful: R1 = R0 (1+alpha(0)t)

that’s it, any advice what so ever would be reallllllly helpful, thanks

There is very little point in our doing your homework for you, since you will not have learnt anything if all we do is give you the answers.

Question 2:

DMM I assume refers to a digital multimeter – this is going to measure things like voltage and current – which of those questions refers to the measurement of voltage?

CRO I assume refers to a cathode ray oscilloscope – this displays the shape of a waveform.  Which of those questions are about observing the overall shape of a waveform being generated?

The answer to both of those is fairly straight forward, but I will leave it for you to take a moments thought about it.

Question 3 seems to have given you an equation, and the values to put into the equation – all it takes is to put those numbers into the equation and get the result (R0 would be the resistance you know, t is the difference in temperature, and R1 is the resistance that would be true when the temperature is reached).

George

#### jezza

• Jr. Member
• Posts: 36
##### Re: i reaaaaally need some help here!
« Reply #2 on: 02/06/2006 04:21:13 »
cool, that helps, thank you

#### The Naked Scientists Forum

##### Re: i reaaaaally need some help here!
« Reply #2 on: 02/06/2006 04:21:13 »