Questions and Answers
Name one common application of Joule’s heating in everyday devices.
Electric toasters are a common application of Joule’s heating.
Why is tungsten used for making bulb filaments?
Tungsten is used because it has a high melting point of 3380°C.
How does a fuse protect electric circuits?
A fuse melts when the current exceeds a specified limit, breaking the circuit.
What type of gases are commonly used in electric bulbs to prolong filament life?
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In what configuration is a fuse typically placed in an electric circuit?
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What happens to the temperature of a fuse wire when a current larger than its rated value flows through it?
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Why is thermal isolation important for a bulb filament?
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Study Notes
Battery and Cell Functionality
- Batteries or cells serve as sources of electrical energy through chemical reactions.
- The potential difference generated between terminals drives the flow of electrons, creating electric current.
Current Maintenance and Energy Expenditure
- Continuous current flow requires the source to expend energy.
- A portion of the source energy can perform useful work (e.g., powering electric fan blades).
- Another portion dissipates as heat, raising the temperature of the device (e.g., electric fan becoming warm with prolonged use).
Heating Effect of Electric Current
- In a purely resistive circuit (only resistors connected to a battery), all source energy is converted to heat.
- This phenomenon is known as the heating effect of electric current and is utilized in appliances like electric heaters and irons.
Work Done and Power Calculation
- For a current I flowing through a resistor R, with potential difference V across it, the work done moving a charge Q is given by VQ.
- The energy supplied by the source over time t must equal VQ.
- Power input to the circuit is defined by the relationship between voltage (V), current (I), and resistance (R).
Heat Generation in Conductors
- Electric current inevitably generates heat in conductors, impacting circuit components.
- Unwanted heat can alter properties of components, but also has useful applications.
Applications of Joule's Heating
- Common devices utilizing Joule's heating include:
- Electric laundry irons
- Electric toasters
- Electric ovens
- Electric kettles
- Electric heaters
Electric Bulbs
- Electric bulbs utilize Joule's heating to produce light.
- Filament needs to retain heat to emit light while avoiding melting at high temperatures.
- Tungsten, with a melting point of 3380°C, is typically used for filaments.
- Filaments are thermally isolated for efficiency, supported by insulation.
- Bulbs are filled with inert gases like nitrogen and argon to enhance filament lifespan.
- Most electric power consumed by the filament produces heat, with a small portion converted to light.
Fuses in Electric Circuits
- Fuses protect circuits by interrupting flow during excessive current.
- Placed in series with devices, fuses stop currents that exceed rated values.
- Made from metals or alloys with specific melting points, such as aluminum, copper, iron, or lead.
- When excess current flows, fuse wire heats up, melting to break the circuit.
- Typically encased in porcelain or similar materials, featuring metal ends.
- Common fuse ratings for domestic use include 1 A, 2 A, 3 A, 5 A, and 10 A.
Practical Example
- An electric iron using 1 kW at 220 V operates a current of approximately 4.54 A.
- Therefore, a 5 A fuse is appropriate for this appliance to ensure safety.
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Description
This quiz covers the fundamental principles of battery and cell functionality, as well as the heating effects of electric current. Explore how energy is maintained and expended in electric circuits and learn about power calculation in resistive components. Perfect for students looking to deepen their understanding of electrical concepts.
