G10 Term 1 Review - Electricity

G10 Term 1 Review - Electricity

by Eko Febianto

​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.

Multiple Choice

What subatomic particles would you find in the nucleus of an atom?

• Protons only
• Protons and Neutrons
• Neutrons and Electrons
• Protons and Electrons 

Multiple Choice

Which of the following can move from one atom to another?

• protons

• neutrons

• electrons

• the nucleus

Multiple Choice

What is a static charge?

• an electric charge that is unchanging

• an electric charge that is fluctuating

• an unbalanced charge on an object

• a balanced charge on an object

Multiple Choice

An object with a negative charge will be most strongly attracted to which of the following?

• an object with a weak positive charge

• an object with a strong positive charge

• an object with a weak negative charge

• an object with a strong negative charge

Multiple Choice

If a substance has an excess number of electrons on its surface, what type of charge does it have?

• A negative charge
• A positive charge
• A neutral charge
• A nuclear charge

Multiple Choice

If an object has the same number of positive and negative charges, its electrical charge is...

• positive
• negative
• neutral or no charge
• opposite

​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

​

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

𝑷 = 𝑽𝑰

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

𝑬 = 𝑽𝑰𝒕

Multiple Choice

An electric bulb is connected to a 220V generator. The current is 0.50 A. What is the power of the bulb?

• 440 W

• 110 W

• 55 W

• 0.0023 W

Multiple Choice

What is the power of a 20V bulb with 5A through it?

• 100W
• 100V
• 6.3W
• 6.3A

Multiple Choice

measure of power

• volt

• ohm

• watt

• amp

Multiple Choice

Charging takes 110 minutes and causes a total charge of 180 000 C to pass through the battery. What is the average charging current in the battery?

• 1636 A

• 163.6 V

• 27 A

• 27 V

Multiple Choice

The current in a motor is 2.1 A and the potential difference across it is 12V. The motor takes 1.5 seconds to lift a mass. What is the energy transferred to the motor as it lifts the mass?

• 85 J

• 3.8 J

• 38 J

• 8.5 J