Podcast
Questions and Answers
What distinguishes direct current (DC) from alternating current (AC)?
What distinguishes direct current (DC) from alternating current (AC)?
- DC flows back and forth.
- AC always flows in one direction.
- AC has a constant voltage.
- DC flows in one direction. (correct)
How is frequency calculated in electrical circuits? (where T is the period of the waveform)
How is frequency calculated in electrical circuits? (where T is the period of the waveform)
- f = 1/Current ​
- f = 1/Voltage ​
- f = 1/T (correct)
- f = T/1
What formula represents the power supplied to an electrical device?
What formula represents the power supplied to an electrical device?
- $P = I + V$
- P = E x t
- P = V × I (correct)
Which wire in a 3-pin plug is correctly associated with its function?
Which wire in a 3-pin plug is correctly associated with its function?
What is the correct method to find the fuse rating needed for a device?
What is the correct method to find the fuse rating needed for a device?
What does the formula $E = P imes t$ represent in an electrical context?
What does the formula $E = P imes t$ represent in an electrical context?
What happens when charge flows through a resistor?
What happens when charge flows through a resistor?
If an appliance has an efficiency of 80% and an input power of 200 W, what is the useful energy used?
If an appliance has an efficiency of 80% and an input power of 200 W, what is the useful energy used?
How do you find the efficiency?
How do you find the efficiency?
what is potential difference?
what is potential difference?
Flashcards
Electrical Power
Electrical Power
The rate of energy transferred to a component.
Energy Transferred
Energy Transferred
The energy transferred to a component over a time interval.
Domestic Electricity Meter
Domestic Electricity Meter
The measure of how much energy is supplied to an appliance.
Mains Cable
Mains Cable
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Charge Flow
Charge Flow
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Resistor
Resistor
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Energy Conservation in a Circuit
Energy Conservation in a Circuit
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Peak Potential Difference
Peak Potential Difference
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Study Notes
Direct Current (DC) and Alternating Current (AC)
- Direct current (DC) flows in one direction
- Alternating current (AC) reverses its direction of flow repeatedly
Mains Circuit Components
- A mains circuit contains a live wire (alternately positive and negative) and a neutral wire (zero volts)
Peak Potential Difference
- The peak potential difference of an AC supply is the maximum voltage measured from zero volts
Frequency Measurement
- To measure the frequency of an AC supply, measure the time period of the waves, then use the equation frequency = 1/time taken for 1 cycle
Electrical Power and Energy
- Power supplied to a device is the energy transferred to it each second.
- Energy transferred to a device (E) = Power (P) x time (t)
- Electrical power supplied to an appliance (P) = current (I) x voltage (V)
- Correct rating for a fuse (A) = electrical power (watts) / potential difference (volts)
Domestic Electricity Meter
- Measures the total energy supplied.
- Energy supplied to an appliance (E) = Power (P) x time (t) Useful energy = efficiency x energy supplied
Plug and Cable Construction
- Sockets and plugs have stiff plastic casings for electrical insulation.
- A mains cable typically has two or three insulated copper wires within flexible plastic material. Color coding: live wire (brown), neutral wire (blue), earth wire (green/yellow).
- The earth wire is connected to the longest pin in the plug; it grounds the metal casing of the appliance.
Charge Flow and Resistance
- Charge flow (Q) = current (I) x time (t)
- When charge flows through a resistor, energy is transferred and the resistor gets hot
- Energy transferred to a component (E) = voltage (V) x charge (Q).
- Energy supplied to all components equals battery's energy supply in a circuit.
Efficiency Calculation
- Be careful when using efficiency values to calculate output power.
- Convert a percentage efficiency to a ratio by dividing by 100%.
- Multiply the input power by the efficiency ratio to obtain the output power.
Units
- 1 kW = 1000 W
Study Tips
- Understand the parts inside a three-pin plug and the colors of each wire.
- Be familiar with the relationship among charge, current, and time.
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