Physics questions!

[Hutchoo]

A 10 V power supply is used across two separate resistors. The current through one is found to be 0.4 A and through the other 0.5 A. When they are combined in series, what current will flow through them and what is their effective resistance?

How would you do this question?
I don't know how to start it off either >.>

[Whatlol]

ok
so when you have Resistor 1 and the power supply the current is 0.4 A

V = IR
R = V/I
R = 25 ohm

Resistor 2 and power supply current is 0.5 A
R =20 ohm

Now when you put these both into series :
I = V/R
I = 10/45
I =0.22 A

Effective resistance will simply be the sum of the two. so 20+25 = 45 ohm

[Hutchoo]

Ooooh. Thanks heaps I understand the question now.

I have another one that I don't really understand either...

[Whatlol]

Ooooh. Thanks heaps I understand the question now.

I have another one that I don't really understand either...

Ok so one thing you first need to realise is that when you increase resistance, for the same voltage the current will decline.

So for a , you should draw a line in that is sort of half way below R1

I cant exactly do this accurately without a ruler , however to find the effective resistance all you need to do is the following :

since R = V/I

pick a point on each graph, record the voltage and current values then calculate the resistance.

Since they will be placed in series just add the two together.

If you want an accurate graph you can use this resistance value to calculate a current value/values for given voltages. i.e find the current at V = 10 and V = 15, then plot that and draw a line through it.

[Hutchoo]

Uhm, I've googled "How do LED's work?" and I get this: http://electronics.howstuffworks.com/led1.htm
I have no idea what it's talking about =.=
Can someone dumb it down for me?

[schnappy]

All you need to know is that they don't follow ohm's law, the voltage drop across them is a fixed value. (Rather than the supply voltage by the ratio of resistance of the total resistance in the circuit - like a V divider)

From the I-R graph you find the voltage drop across the diode. Also what its current supply should be.

[Hutchoo]

Schnappy, thanks for your help when I needed it

Just a quick question..

I have to make a concept map and one of the key words is "Gray" .... wth is "Gray"? Another key word is "Activity"... what do these means in terms of physics?

This is what it relates to: Fisikz imagez

Thanks in advanced

[schnappy]

Oooo it's been a long time since I've looked at this sort of stuff, and when I did it my school bludges it - the questions I've seen people do on it here are much more thought-intensive than I ever did.

Activity I'm not too sure, but my guess would be that it's just how radioactively active it is. So how unstable the nucleus is.

Grays (I believe it is Grays not Gray) is a unit associated with energy.

grays (Gy) (Gy) are used in measuring the energy of radiation absorbed by the target material in joules per kilogram.

[pi]

+1 to what has been said by schnappy

Activity:

The strength of a radioactive source is called its activity, which is defined as the rate at which the isotope decays. Specifically, it is the number of atoms that decay and emit radiation in one second.

[Hutchoo]

Thanks for that guys, I understand what it means by "gray" now.. Although it's supposed to be "Grays".

Kinda upset that no one realised the image was called "Conception.jpeg" but other than that, THANKKKKKK YOUUUUU.

[Hutchoo]

Uh, how would you work this out :/

[Lasercookie]

Alpha particles are equivalent to
Gamma rays are  , so they have pretty much no effect on the mass/atomic numbers.

So in 4a,

so,

so,

Refer to periodic table, element with Atomic number 82 is Lead, so:



The rest of the question is basically the same process, but with b and d, they've used shorthand notation:
is the same as:

[schnappy]

An alpha decay is the loss of a Helium-4 nucleus (Loss of 2 neutrons, 2 protons, so mass # goes down 4 and atomic # down by 2).
a)
Po has undergone alpha/gamma decay (gamma is just a photon - energy. No mass change), but the alpha particle has stolen 2 neutrons and 2 protons from the Po. The new atomic number is 82, and mass number 214. So it's Lead-214.

I hope.

Edit: So I have to do B then

b)
Uranium has been kindle given an alpha particle to live with, so has gained 2 protons and 2 neutrons. The new atomic number is (92+2=94), and its mass number is (235+4=239). X must be Plutonium-239. Mmmm, nuclear weapons.

[Thu Thu Train]

Rules for decay:




I'm confused about the beta decay though because there are two types of beta decay and this one doesn't say which one it is.

[Hutchoo]

<3 <3 <3

THANKS

EDIT: Your DP scares me, comeatmebrah.