Chapter 10 To 11

Question 1

Why are volts lost

Answer 1

Whenever there is a current, work hadnti be dine by the charges, and some energy is always lost as heat

Thus you lose some voltage and this is terminal pd

Question 2

Internal resistance equations and what happens when current increases

Answer 2

Kircooff second law means emf = V + termnal pd , which is Ir
V= IR
So e= IR + Ir

If r is cinstant, an increase of current increases the volatage lost and lowers terminal pd

Question 3

If something needs high currents, what will internal resistance be
And if you want emf to = terminal what yiundo

Answer 3

1) very low

2) current needs ti be 0 (remember extrapolation)

Question 4

Explain v against current graph and where it comes from

Answer 4

E= IR + Ir
V= -Ir + En, thisnis the equation

Essentially as current increases, the lost volts increase too, so voltage decreases,
When current is 0 , terminal PD= emf, so y intercept is emf
Y which is v = -rx , so internal resistance is negative r

If they say double emf draw same gradient wimes two higher, double internal resistnce half the graduent (half as steep)

Question 5

What items have high internal resistance and which have low

Answer 5

Sonsomething with low gives higj currrents, recharbela batteries in ohones erc cars have this, so you can recharge without overheating or wasting a lot of energy

But something that needs to be safe like classrooms or high volatage suplly uses high so thwt currents are low

Question 6

What makes a good sensing circuit

Answer 6

• firdt redistances have tinbebhuge donpower output idnlow due to low current and thus heat is low
• need current to be not too small or radiowaves will interefere
• you need both resistances to be matched , or else it wint make thwt much difference if really small or big (as it is parallel circuit and follows 1/r rule)
• finalky starting reistance needs to be half way so that you get maximum swing of voktage

Question 7

Potentiometer ?

Answer 7

Is a vairble resistor with three terminals and a sliding contact point

• adjusting this adjusts pd let out ,
• adavnatge is that it provided fukk swing of resistance so fukk swing if voltage can be emasured here
• works by wires coated in olastic so cant go across wire but fan go through upwarde

Question 8

Two advantages if using potentiometer over potenial dividwr

Last point

Answer 8

1) can be very compact good for small devices
2) reisstance full swing and can change lineraly or logarithmicaly

Allows V Out to be VARIED AT A SPECFIC TEMP rather than having to make new circuits again and again

Question 9

How to manipulate batteries to get higher or lower currents? For internal resistance

Answer 9

If put in series you add the emf but also the resistance - eventually this decreases current
Lid you add in parallel keep emf same but reduce resistance= increase current

So if want to increase current = parallel, decreased = series

Question 10

How to find graph experiment of internal residtsnce

Answer 10

• ammeter voltmeter and variable resistor connect to battery
• change resistance to get different amps and plot against terminal pd
  Use graph to findniutnvalued

Question 11

What happens to internal resistance as current gets too high?

Answer 11

Increase due to temp, don’t do this