​Electric Charge

• ​There are 2 types of charges: positive and negative.

• Unlike charges attract and like charges repel.

• Electric field: region in which electric charge experiences a force

• Conductors: materials that let electrons pass through them.

  • Metals are the best electrical conductors as they have free electrons.

• Insulators: materials that hardly conduct at all. Their electrons are tightly held to atoms and hardly move, but they can be transferred by rubbing

• The SI unit of charge is the Coulomb (C).

​Electric Charge

• ​A charge that “appears” on an uncharged object because of a charged object nearby

  • For example, if a positively charged rod is brought near a small piece of aluminum foil, electrons in foil are pulled towards rod, which leaves the bottom of the foil with a net positive charge.

    The attraction is stronger than repulsion because the attracting charges are closer than the repelling ones.

​Basic Electricity - Current

• ​Current: a flow of charge, the SI unit is the Ampere (A).

• An ammeter measures the current in a circuit and is connected in series

• Current is a rate of flow of charge.

• 𝐶ℎ𝑎𝑟𝑔𝑒 (𝐶) = 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 (𝐴) × 𝑇𝑖𝑚𝑒 (𝑠)

𝑄 = 𝐼𝑡

• Current follows path of least resistance

​Basic Electricity - E.M.F

• The maximum voltage a cell can produce is called the electromotive force (EMF), measured in volts.

  When a current is being supplied, the voltage is lower because of the energy wastage inside the cell.

  A cell produces its maximum PD when not in a circuit and not supplying current.

​Basic Electricity - P.D

• Potential difference, or PD for short, is also known as voltage.

  Voltage is the amount of energy the cell gives the electrons it pushes out.

• Voltage is measured in volts (V) and is measured by a voltmeter (connected in parallel).

• If a cell has 1 Volt, it delivers 1 Joule of energy to each coulomb of charge (J/C).

​𝑉𝑜𝑙𝑡𝑎𝑔𝑒 = 𝐸𝑛𝑒𝑟𝑔𝑦 / 𝐶ℎ𝑎𝑟𝑔𝑒

𝑉 = 𝐸/ 𝐶

​Basic Electricity - Resistance

𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 (Ω) = 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 / 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 = 𝑉/𝐼

​

Factors affecting resistance:

• Length - 𝑅 ∝ 𝐿

• Cross-sectional area - 𝑅 ∝ 1/𝐴

• Material - Better conductor = less resistance

• Temperature

  • For metal conductors higher temperature = more resistance

  • For semi-metal conductors higher temperature = less resistance

​Basic Electricity - Electrical Energy

1 Watt is 1J/s

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𝐸𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑎𝑙 𝑝𝑜𝑤𝑒𝑟 = 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 (𝑉) × 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 (𝐴)

𝑷 = 𝑽𝑰

𝐸𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑎𝑙 𝑒𝑛𝑒𝑟𝑔𝑦 = 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 (𝑉) × 𝐶𝑢𝑟𝑟𝑒𝑛𝑡 (𝐴) × 𝑡𝑖𝑚𝑒 (𝑠)

𝑬 = 𝑽𝑰𝒕