STPM Physics Chapter 14 Electric Current

STPM PHYSICS CHAPTER 14 ELECTRIC CURRENT

SMK SACRED HEART, SIBU

1. Electric current , I = Rate of flow of charge, = (rate of flow of electrons) x (charge of electrons), xe as Q = Ne = It = nAve or Ave I=

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9. Doping of semiconductor Types Element Charge carriers n-type Group 15 (Phosphorus) Electrons p-type Group 13 (Boron) Holes 10. Graph of resistance (or resistivity) temperature

x e = nAve or Ave

2. Drift velocity, v = mean velocity of the free electrons towards the positive terminal. 3. Current density, J = Current per unit cross-sectional area, J = = nve = 4. Electrical conductivity, = ratio of current density to the electric field strength , 5. Resistivity of a material, = resistance of 1 metre length of the wire that has a cross-sectional area of 1m2

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6. Ohm’s law = current through a given conductor is directly proportional to potential difference between its end points.

11. Power equation P = IV = I2R =

12. Manipulating resistivity question: - Resistivity of material is constant for the same type of material regardless of the change in crosssectional area

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Ohm’s law : I V For ohmic conductor: V = IR 7. Temperature coefficient, = change in resistance per unit resistance per unit degree change of temperature.

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8. For conductors: - When T increases, R increases, decreases - Number of electrons remain unchanged - Metal ions vibrate faster with greater amplitude (distance between two metal ions, s decreases) - Dispersion of free electron occurs - Drift velovity of electron decreases, v = - Mean time between collisions of the free electrons decreases

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