Resistance

Question 1

How does one calculate series resistance

Answer 1

V = I × R
V is the potential difference in volts, V
I is the current in amperes (amps), A
R is the resistance in ohms, Ω

In series add all resistance together

Question 2

There is a direct relationship between voltage, current and resistance. State the law that applies. Quote the law and the equation

Answer 2

This fundamental principle is known as Ohm’s Law which states: ‘the value of a current passing through a conductor is directly proportional to the potential difference between the ends of the conductor, and inversely proportional to the resistance of the conductor’. The ohm is defined as a resistance between two points of a conductor This can be expressed mathematically by the following equations V = A X R or R = V/A

Question 3

The resistance of a circuit, which is measured in Ohms, depends on a number of factors, namely:

Answer 3

(i) The length of a conductor. An increase in length results in an increase in resistance. (ii) The cross-sectional area of the conductor. The greater the cross-sectional area, the lower the resistance. (iii) The conductivity of the material used. Some materials are better conductors than others (e.g., silver is a better conductor than copper). (iv) Temperature. For most materials, the hotter the material, the greater its resistance.

Question 4

how does one calculate with a circuit in parrallel

Answer 4

1. Consider each branch and calculate each with ohms law
2. add currents together to give total ammount of current
3. apply Ohms law using total figure

Question 5

Answer 5

The wheel above is divided into three sections:

Volts V (on top of the dividing line)
Amps (amperes) I (lower left below the dividing line)
Resistance R (lower right below the dividing line)
X represents the (multiply by sign)
Memorize this wheel

To use, just cover the unknown quantity you need with your minds eye and what is left is the formula to find the unknown.

Question 6

what is resistivity

Answer 6

quantifies how strongly a given material opposes the flow of electric current. A low resistivity indicates a material that readily allows the movement of electric charge. Resistivity is commonly represented by the Greek letter ρ (rho). The SI unit of electrical resistivity is the ohm⋅metre (Ω⋅m)

Question 7

Formula for RESISTIVITY

Answer 7

R = ρl/ A

Where:.

R = resistance (Ω)

ρ = resitivity of the material (Ω m)

I = length of wire (m)

A = cross-sectional area of the wire (m2)