resistance and resistivity Flashcards

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1
Q

Why use gold in circuits

A

Excellent conductor

number density almost as high as copper

much less reactive so corrodes very little over time

used in high energy electrical applications

and fine wires that connect pins on computer chips to integrated circuit boards

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2
Q

4 factors of resistance

A

Temperature

Material

length of wire

cross sectional area of the wire

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2
Q

Is resistance or resistivity unique

A

resistivity of a material is unique

ie copper has a unique resitivity

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3
Q

what does term resitivity mean

A

used to describe electrical property of material

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4
Q

What happens to PD and RESISTANCE when length of wire doubles

and whats proportionality of resistance and length

A

PD doubles too x2, So resistance doubles

restiance proportional to length

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5
Q

What is relationship between Resistance and length in terms of poroportionality

A

Resistance is directly proportional to length

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6
Q

What happens if cross sectional area of wire increases

A

resistance decreases

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7
Q

Whats proportionality relationship between resistance and cross sectional area

A

Resistance is inversly proportional to 1/A

R= 1/A

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8
Q

What is the equation for restitivity and resistance and the name of the symbol for restitivity.

and significance of each letter in equation

A

R = PL/A

P= RA/L

p is rho symbol

R is resitance
A is area
L is length

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9
Q

What is resitivity measured in

A

ohm metre

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10
Q

what is the equation needed to calculate cross sectional area

A

pie r squared

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11
Q

What happens to resitivity when temps increase

A

Resistivity increases

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12
Q

How to do resitivity experiment

A
  1. Make a circuit with terminal, ammeter,voltmeter
  2. Use a piece of wire, and investigate restistance by changing the length of wire, and see the PD across those lengths and the current to get Resistance
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13
Q

how to determine resistivity from the values obtained from experiment

A
  1. First draw line, it will be a linear line through origin. Y axis is resistance R, x axis is length/m
  2. Get gradient
  3. Gradient = R/L
  4. Gradient x cross sectional area of wire = resitivity
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14
Q

What is superconductivity

A

When material gets colder, their resistivity drops as expected. But then at a critical temperature the resistivity suddenly falls to 0.

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15
Q

do components made of superconducting material have electrical resistance

And the effect of this

A

No, which is why huge amounts of current passes through them.

16
Q

What is the typical temperature at which wires become superconducting

A

4 Kelvin = -269 celcius

17
Q

What is the typical temperature for superconductors

A

4 Kelvin = -269 celcius

18
Q

What is the difference between resistance and resistivity

A

Resistivity is a property of a material that only changes if temperature changes. Measured in ohm metres

Resistance is dependant on resisitivity ie material, area and length of component. measured in ohms