Need answers for Physics questions

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Sheepie4Real
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#1
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I was recently handed a sheet by my physics teacher to complete but then she forgot about it and I would like the answers so that I can check it myself. I believe the sheet is pages 216-217 for the 'Advanced Physics For You' book, but I'm not that certain. Any help with Q1-3 would be nice as I'm certain about the answers for the others. Thanks.
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Mayhem™
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(Original post by Sheepie4Real)
I was recently handed a sheet by my physics teacher to complete but then she forgot about it and I would like the answers so that I can check it myself. I believe the sheet is pages 216-217 for the 'Advanced Physics For You' book, but I'm not that certain. Any help with Q1-3 would be nice as I'm certain about the answers for the others. Thanks.
Look up the answers for the book online?
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Sheepie4Real
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(Original post by Mayhem™)
Look up the answers for the book online?
I found the book on google books but the free preview omitted those pages.
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Absent Agent
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(Original post by Sheepie4Real)
I was recently handed a sheet by my physics teacher to complete but then she forgot about it and I would like the answers so that I can check it myself. I believe the sheet is pages 216-217 for the 'Advanced Physics For You' book, but I'm not that certain. Any help with Q1-3 would be nice as I'm certain about the answers for the others. Thanks.
I think if you post the questions with your working then somebody will be able to help/check them for you.
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Sheepie4Real
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(Original post by Mehrdad jafari)
I think if you post the questions with your working then somebody will be able to help/check them for you.
Ok
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Sheepie4Real
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Q1 (Fill in the blank exercise)
a) In a series circuit, the current through each component in the circuit is the same
b) For resistors in series, the total voltage is the sum of the p.d.s across the separate resistors
c) In a parallel circuit, the current in the main circuit is equal to the sum of the currents in the branches
d) For resistors in parallel, the voltage across each resistor is the same
e) Kirchhoff’s second law states that around any closed loop in a circuit, the sum of the emfs is equal to the sum of the current and resistance.

The words in bold are the words I put in the blanks.
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Sheepie4Real
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Q2 Explain why combined resistance of two resistors in parallel is always less than either of the separate resistances.

When two resistors are connected in parallel, the resistance of the circuit is given as: 1/RT = 1/R1 + 1/R2 This means that to get the resistance of the circuit the resistance of the resistors must be taken as a reciprocal and combined. The answer given through this method needs to be taken as a reciprocal too so the resistance of the circuit (the two resistors combined) is less than either of the separate resistances of the separate resistors.
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Absent Agent
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(Original post by Sheepie4Real)
Q1 (Fill in the blank exercise)
a) In a series circuit, the current through each component in the circuit is the same
b) For resistors in series, the total voltage is the sum of the p.d.s across the separate resistors
c) In a parallel circuit, the current in the main circuit is equal to the sum of the currents in the branches
d) For resistors in parallel, the voltage across each resistor is the same
e) Kirchhoff’s second law states that around any closed loop in a circuit, the sum of the emfs is equal to the sum of the products of the currents and resistances.

The words in bold are the words I put in the blanks.
To my knowledge, I think they are correct except for e) in which case you should mention the word product, since the total e.m.f around a closed loop is e.m.f_{total} = I (R+r)

(Original post by Sheepie4Real)
Q2 Explain why combined resistance of two resistors in parallel is always less than either of the separate resistances.

When two resistors are connected in parallel, the resistance of the circuit is given as: 1/RT = 1/R1 + 1/R2 This means that to get the resistance of the circuit the resistance of the resistors must be taken as a reciprocal and combined. The answer given through this method needs to be taken as a reciprocal too so the resistance of the circuit (the two resistors combined) is less than either of the separate resistances of the separate resistors.
I'm not really sure how the examiners would expect you to answer this question but your reasoning is correct. I think you could also show this mathematically by working out the total resistances in each form of circuit and compare them. For example:

The total R in a series circuit of three equal resistances is Rtotal=R+R+R=3R
But in a parallel circuit \dfrac{1}{R_{total}} = \dfrac{1}{R} + \dfrac{1}{R} + \dfrac{1}{R} = \dfrac{3}{R}

Therefore the R_{total} = \dfrac{R}{3}

Comparing the total resistances in each circuit,  3R > \dfrac{3}{R}
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