Basic Science and Technology - Junior Secondary 3 - Electrical energy

TERM: 2^ND TERM

WEEK: 9

CLASS: Junior Secondary School 3

AGE: 14 years

DURATION: 40 minutes each for 2 periods

DATE:

SUBJECT: Basic Science

TOPIC: Electrical energy

SPECIFIC OBJECTIVES: At the end of the lesson, the learners should be able to

1. ) Define electrical energy
2. ) Describe the flow of electrons and its types
3. ) State and explain the two ways in which an electrical circuit can be set up with diagrams
4. ) Explain ammeter, voltmeter, fuse and circuit breaker
5. ) Explain electrical meter and its types
6. ) Perform calculations on meter reading and billing

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, story-telling, videos from source

INSTRUCTIONAL MATERIALS: Recommended Basic Science textbooks for Junior Secondary School 3

INSTRUCTIONAL PROCEDURES: PERIOD 1-2:

NOTE

ELECTRICAL ENERGY

Electrical energy is the energy that results from the flow of electric charge (electricity) through a conductor. It is commonly used to power devices and appliances in homes, industries, and various other sectors. Electrical energy is measured in joules (J) or kilowatt-hours (kWh) when used over time.

Flow of Electrons
The flow of electrons refers to the movement of negatively charged particles (electrons) through a conductor, typically a wire, when an electric field is applied. The types of electron flow are:

• Direct Current (DC): In DC, electrons flow in one direction only, from the negative terminal to the positive terminal. Examples of DC sources are batteries and solar cells.
• Alternating Current (AC): In AC, the direction of electron flow alternates periodically. The current flows in one direction for a fraction of a second and then reverses direction. This type of current is commonly used in household electricity supply.

Ways to Set Up an Electrical Circuit:

• Series Circuit: In a series circuit, all components (resistors, lamps, etc.) are connected end-to-end, forming a single path for the current to flow. If one component fails or is disconnected, the entire circuit is broken.

• Parallel Circuit: In a parallel circuit, components are connected across multiple paths. Each component has its own separate path to the power source, meaning if one component fails, the others continue to work.

Ammeter, Voltmeter, Fuse, and Circuit Breaker:

• Ammeter: An ammeter is a device used to measure the current (flow of electrons) in a circuit. It is connected in series with the component whose current is to be measured.
• Voltmeter: A voltmeter measures the potential difference (voltage) between two points in a circuit. It is connected in parallel with the component across which the voltage is being measured.
• Fuse: A fuse is a safety device that protects electrical circuits from overloads or short circuits. It contains a thin wire that melts when the current exceeds a safe level, disconnecting the circuit to prevent damage.
• Circuit Breaker: A circuit breaker is an automatic switch that stops the flow of current in the event of a fault or overload. It can be reset once the issue is resolved, unlike a fuse, which needs to be replaced.

Types of Electric Meters

Electrical meters are essential devices that measure the amount of electrical energy consumed by a household or business. These meters can be classified into prepaid and postpaid systems based on how electricity consumption is billed. Below is a discussion of each type:

1. Prepaid Meters:

Prepaid meters require customers to pay for electricity upfront before consumption. Essentially, the consumer purchases credit, which is then loaded onto the meter. The electricity supply is cut off once the credit runs out, and the customer needs to top up by purchasing more credit.

How It Works:

• Customers buy electricity credits (usually in kWh or local currency equivalent) from approved vendors or directly through mobile apps or online platforms.
• The credits are loaded into the prepaid meter via a token, card, or digital means.
• As electricity is consumed, the available credit decreases, and once it is exhausted, the meter disconnects the power supply, requiring the customer to load more credit to restore service.

Advantages:

• Control Over Consumption: Users have direct control over their energy use since they can monitor and manage their remaining credit, avoiding surprise bills.
• No Bills: Since customers pay in advance, there are no monthly bills or post-consumption billing issues.
• Debt-Free Usage: Customers cannot accumulate electricity debt, making it more affordable for those with irregular incomes.

Disadvantages:

• Prepaid Cost: Customers may face upfront costs that need to be managed, especially if they run out of credit unexpectedly.
• Disconnection: If the credit is exhausted, the power is immediately cut off, which may lead to inconvenience if not properly managed.

2. Postpaid Meters:

In postpaid systems, customers consume electricity first and are billed later based on the amount of electricity used during a billing cycle, typically monthly or quarterly. The energy consumption is measured by the meter, and the customer is expected to pay after the consumption is recorded.

How It Works:

• The electricity meter records the total energy consumption during a specific period.
• A meter reader or automated system records the reading, and based on this data, the customer is billed for the total usage.
• Bills are generated at the end of the billing cycle (e.g., monthly), and the customer must pay by the due date.

Advantages:

• No Upfront Payment: Customers do not need to prepay for electricity, which can be more convenient, especially for households or businesses with variable energy use.
• Flexibility: The postpaid system allows for greater flexibility, as customers are not constrained by the need to top up credit frequently.

Disadvantages:

• Bill Shocks: Since the customer consumes energy first and pays later, there may be instances of unexpectedly high bills, leading to financial strain.
• Debt Risk: If customers fail to pay their bills on time, they can accumulate debts, which may lead to disconnections or penalties.

Calculations on Meter Reading and Billing:

Let’s assume a customer has a prepaid meter and buys electricity credits to load onto their meter. The customer has consumed a total of 500 kWh of electricity in one month.

• Electricity Tariff Rate: Let's assume the rate per kWh is ₦50.

Calculation:

• Total consumption = 500 kWh
• Rate per kWh = ₦50

Total amount payable:

Total amount=500 kWh×50 Naira

Total amount=₦25,000

So, the customer would need to load ₦25,000 onto their prepaid meter to cover 500 kWh of electricity usage.

Scenario for Postpaid Meter Calculation:

For a postpaid meter, the electricity consumption over a billing cycle is measured by the meter, and the customer is billed for the total consumption at the end of the month or billing cycle.

Let’s assume the customer’s meter reading shows they have consumed a total of 600 kWh in one month.

• Electricity Tariff Rate: The rate per kWh is ₦50.

Calculation:

• Total consumption = 600 kWh
• Rate per kWh = ₦50

Total amount payable:

Total amount=600 kWh×50 Naira

Total amount=₦30,000

So, the customer would receive a bill for ₦30,000 based on their 600 kWh of consumption for that billing period.

Calculation Example with Variable Tariff:

Sometimes, tariffs can vary based on consumption levels or time of day. If there’s a tiered tariff, the calculation would change accordingly.

Assumption for tiered tariff:

• For the first 200 kWh, the rate is ₦50 per kWh.
• For consumption above 200 kWh, the rate is ₦60 per kWh.

Let’s assume the customer has consumed a total of 400 kWh.

Calculation:

• First 200 kWh: 200 kWh×50 Naira=₦10,000
• Remaining 200 kWh: 200 kWh×60 Naira=₦12,000

Total amount payable:

Total amount=₦10,000+₦12,000=₦22,000

So, the customer would need to pay ₦22,000 for the 400 kWh consumption under a tiered tariff system.

EVALUATION:

1. Explain the difference between direct current (DC) and alternating current (AC), and provide examples of devices that use each type.
2. How does the arrangement of components in a series circuit differ from that in a parallel circuit, and what are the advantages and disadvantages of each?
3. Describe the functions of an ammeter and a voltmeter in an electrical circuit. How should they be connected to measure current and voltage, respectively?
4. What is the purpose of a fuse and a circuit breaker in an electrical system, and how do they protect the circuit from damage?
5. If an electrical meter shows a consumption of 1500 kWh over a billing period, and the rate is ₦75 per kWh, how much will the bill be for that period?

CLASSWORK: As in evaluation

CONCLUSION: The teacher marks their books and commends them positively