شرح درس استخدام الطاقة الكهربائية (٢) فيزياء ثالث ثانوي 1445

Understanding Superconductors and Energy Transfer

Introduction to Superconductors

• The lesson begins with a prayer and an introduction to the topic of superconductors in electrical energy usage.

• It is established that electric current carries energy through wires, which have resistance that limits this flow.

Characteristics of Superconductors

• Superconductors are defined as materials that can conduct electricity without any energy loss, meaning they have zero resistance.

• The absence of resistance in superconductors allows for uninterrupted current flow, eliminating voltage drops across these materials.

Conditions for Superconductivity

• To achieve superconductivity, materials must be cooled to very low temperatures (below 100 Kelvin or -173°C).

Applications of Superconductors

• Practical uses for superconductors include MRI machines and particle accelerators like synchrotrons, which are essential in nuclear energy applications.

Energy Transmission Challenges

Generating Electrical Energy

• Electrical energy is generated at hydroelectric dams or power plants using various fuels.

• This energy is transmitted over long distances (up to hundreds of kilometers), necessitating efficient wire systems.

Power Loss During Transmission

• All conductive wires exhibit some resistance leading to power loss during transmission; this lost power is termed "lost capacity."

• The formula P = I^2 R illustrates how power loss occurs due to the current squared multiplied by the resistance in the wires.

Reducing Power Loss

Strategies for Minimizing Losses

• To minimize power losses during transmission, two main strategies can be employed: reducing resistance or lowering the amount of current flowing through the wires.

Reducing Resistance

• One method involves using thicker wires with larger diameters to decrease their inherent resistance; however, this approach increases costs significantly due to material expenses and structural requirements.

Lowering Current Flow

• Another strategy focuses on reducing the current itself while maintaining overall power levels by increasing voltage instead.

Increasing Voltage for Efficient Transmission

Importance of Voltage Adjustment

• By raising voltage levels at substations after generation, it becomes possible to lower the current flowing through transmission lines effectively.

Implementation in Power Systems

Understanding Electrical Power and Consumption

Voltage Transformation in Power Distribution

• The process of increasing voltage from 10,000 volts to 100,000 volts reduces current significantly, leading to lower power consumption.

• In Saudi Arabia, voltage is reduced in stages: first to 10,000 volts for industrial use, then further down to 220 or 240 volts for residential applications.

Energy Loss and Resistance

• Electrical wires have resistance that leads to energy loss; this is quantified by the formula P = I^2 times R .

• To minimize energy loss, either reduce resistance (using high-conductivity materials) or decrease current by raising voltage through transformers.

Billing Mechanism for Electricity Consumption

• Electricity companies sell energy measured in kilowatt-hours (kWh), which represents the total energy consumed over time.

• The term "power" refers to the rate of energy delivery over time; thus, billing is based on actual energy usage rather than instantaneous power.

Understanding Kilowatt-Hour (kWh)

• A kilowatt-hour equals a continuous power consumption of 1,000 watts over one hour (3,600 seconds). For example:

• Ten light bulbs at 100 watts each consume 1 kWh if left on for an hour.

• A heater rated at 1,000 watts consumes 1 kWh when operated for one hour.

Cost Calculation of Electricity Usage

• In Saudi Arabia, the cost per kWh is approximately 18 SAR. This price can fluctuate over time.

• To calculate costs: multiply the number of kWh consumed by the unit price. For instance:

• If a device uses a certain amount of kWh over a period, you can determine its cost using this formula.

Superconductors and Energy Efficiency

• Superconductors are materials with zero resistance that allow electricity flow without energy loss but require cooling below critical temperatures (below ~100 Kelvin).

• Applications include MRI machines and particle accelerators where efficient electrical conduction is crucial.

Reducing Energy Losses in Transmission

• To minimize losses during transmission:

• Reduce wire resistance through larger diameter conductors or higher conductivity materials.

• Alternatively, lowering current by increasing voltage while maintaining power levels is more effective and economical.

Practical Examples of Energy Consumption Calculations

• When calculating total energy consumption:

• Example: Operating ten light bulbs at 100 watts each continuously for an hour results in consuming only one kilowatt-hour.

Real-Life Application Scenarios

• For practical calculations involving devices like heaters:

Calculating Costs and Power Consumption

First Problem: Cost Calculation

• The cost is calculated by multiplying the number of units consumed (270) by the unit price (18 Riyals), resulting in a total of 4860 Riyals.

• To find the current flowing through a digital clock's resistance, Ohm's law is applied: I = V/R, where V is 115 volts and R is 12000 ohms, yielding approximately 9.6 mA.

• The power consumption (P) of the clock can be calculated using P = I × V; substituting values gives about 1.1 Watts.

• To determine the operational cost over 30 days, convert power from watts to kilowatts by dividing by 1000 and multiply by time (30 days × 24 hours).

• The final cost calculation results in approximately 14 Riyals for operating the clock for a month.

Second Problem: Battery Charging Time

• A car battery requires more energy to recharge than it discharges; specifically, it needs to be charged with a current that is 1.3 times greater than its discharge rate due to efficiency losses.

• The charging time can be derived from the relationship between current and voltage during charging and discharging phases.

• By equating currents during charging and discharging, calculations show that if discharged at a high rate (55 Amps), recharging occurs at a lower rate (7.5 Amps).

• This discrepancy leads to longer charging times compared to discharging times; while it takes an hour to discharge fully, recharging may take up to six hours or more.

Conclusion