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Main ObjectiveWe now consider situations involving electric charges that are in
motion through some region of space
❑ Although the charges are discrete object,
they can still be considered as continuous variable
because number of charged particles under treatment is very large.
Instantaneous current
Resistance and Resistors• The circuit elements that control the amount of current is called resistor.
• Resistance of a wire is given by
• 𝑅 ∶ 𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒, 𝝆:𝑹𝒆𝒔𝒊𝒔𝒕𝒊𝒗𝒊𝒕𝒚, 𝑙: 𝑙𝑒𝑛𝑔𝑡ℎ, 𝐴: 𝑐𝑟𝑜𝑠𝑠 − 𝑠𝑒𝑐𝑡𝑖𝑜𝑛𝑎𝑙 𝑎𝑟𝑒𝑎
𝑹 = 𝝆𝒍
𝑨
❑ The resistivity is the inverse of the conductivity 𝝆 = Τ𝟏 𝝈
Ohmic vs Nonohmic Materials
❑ (a) The current–potential difference curve for an ohmic material.
The curve is linear, and the slope is equal to the inverse of the resistance of the
conductor.
❑ (b) A nonlinear current–potential difference curve for a junction diode.
This device does not obey Ohm’s law.
➢ Temperature dependency of
the resistivity of common conductors
➢ Temperature dependency of
the resistivity of superconductors
Comparison of the temperature dependencies of the resistivity of conductors and semiconductors
As temperature increases
• In conductors, the number of collisions between charges increases in conductor,
thus decreasing the drift speed
• In semiconductors, the number of charge carriers increases;
More electrons are available in the conduction band due to a decrease in the band gap
0,0698𝑥35 ≈ 2,4 𝑘𝑟
In reality, the cost is higher because some energy is
transferred from the water into the surroundings by heat and
electromagnetic radiation while its temperature is
increasing.
• If you have electrical devices in your home with
power ratings on them, use this power rating and
an approximate time interval of use to estimate the
cost for one use of the device.