# questions in physics help

• Dec 11th 2010, 10:10 AM
r-soy
questions in physics help
1 – What is the relation between the main current which flows from the source and the current in each resistor in series ?
The current is same for each resistor in series

2 – What is the relation between the potential difference across the source and the potential differences across each resistor in series ? Which resistor has the highest pd across it ?
potential difference will divide for each resistor in series
the highest pd highest. .. which has lees are

3- A potential difference of 12 V is found to produce a current of 0.40 A in a 3.2 cm length of wire with a uniform radius of 0.40 cm what is the resistance and resistively of wire ?R= V/I
= 12 / 0.40 = 30 Ω

4 – A 3Ω resistor a 6 Ω resistor and 9 Ω resistor are connected in series with a 12 V battery .
Draw a circuit diagram . What are
A ) the equivalent resistance
b) the current in each resistor
c ) the pd across each resistor

A) R = R1 + R2 + R3
18 Ω

B ) I = V/R = 18/12 =1.5 A

C ) V= IR
= 1.5 X 18 == 27
• Dec 11th 2010, 10:27 AM
CaptainBlack
Quote:

Originally Posted by r-soy
1 – What is the relation between the main current which flows from the source and the current in each resistor in series ?
The current is same for each resistor in series

2 – What is the relation between the potential difference across the source and the potential differences across each resistor in series ? Which resistor has the highest pd across it ?
potential difference will divide for each resistor in series
the highest pd highest. .. which has lees are

Since the current $i$ is the same through each resistor we have for the $k$ th resistor (from Ohm'd law):

$V_k=i R_k$

that is the potential drop across each is proportional to its' resistance.

CB
• Dec 11th 2010, 10:32 AM
CaptainBlack
Quote:

Originally Posted by r-soy

3- A potential difference of 12 V is found to produce a current of 0.40 A in a 3.2 cm length of wire with a uniform radius of 0.40 cm what is the resistance and resistively of wire ?R= V/I
= 12 / 0.40 = 30 Ω

You are also asked for the resistivity, which in this case is:

$\displaystyle \rho=R\frac{A}{l}$

where $A$ is the crossectional area of the wire and $l$ is its' length.

CB
• Dec 11th 2010, 10:35 AM
CaptainBlack
Quote:

Originally Posted by r-soy
4 – A 3Ω resistor a 6 Ω resistor and 9 Ω resistor are connected in series with a 12 V battery .
Draw a circuit diagram . What are
A ) the equivalent resistance
b) the current in each resistor
c ) the pd across each resistor

A) R = R1 + R2 + R3
18 Ω

B ) I = V/R = 18/12 =1.5 A

C ) V= IR
= 1.5 X 18 == 27

A and B are OK, but C asks for the voltage drop across each resistor, so there are three voltages required, and the answer to (2) tells you their ratios and 4A their sum

CB