Untitled Quiz

Electric Circuits

• Electric circuits can be drawn using standard symbols and notations
• It's important to know and be able to differentiate between voltage, current, and resistance
• Rules for parallel and series circuits can be applied to calculate equivalent resistance, currents, and voltages
• Current and voltage inside electric circuits can be measured
• Electrical energy and electrical power can be calculated

Electric Sockets in Switzerland

• An ordinary electric socket in Switzerland has three poles that can be distinguished
• It is important to differentiate between AC and DC
• Electric shocks can cause health risks
• Safety measures such as circuit breakers, RCDs, and protective earth should be understood

Electric Current

• Electric current (I) indicates the amount of charge (ΔQ) that flows through a conductor in a time interval (Δt)
• Formula: I = ΔQ/Δt
• SI unit of current is Ampere (A): [I] = A = C/s
• Current consists of free-moving charges that can be positive or negative

Technical vs. Physical Current Direction

• Technical current direction flows from positive to negative
• Physical current direction depends on the charge particle
• In most situations, the charges are electrons that freely move in metals

Resistance

• Resistance (R) is defined with current (I) and voltage (V): R = V/I
• SI unit for electrical resistance is Ohm (Ω): [R] = Ω = V/A

Voltage

• Electric voltage is the electric potential difference between two points (A and B) in an electric field
• Represented as VAB = ØB - ØA
• Work done to transfer a charge (q) in an electric field from A to B is given by: WAB = q * VAB
• If the electric field is generated by a point charge, the voltage is expressed by: VAB = ke * Q * (1/rB - 1/rA)

Ohmic Resistor

• Applies to an ohmic resistor: R = V/I = constant

Parallel Circuits

• The equivalent resistance (Req) of multiple resistors (R1, R2, ..., Rn) connected in parallel: 1/Req = 1/R1 + 1/R2 + ... + 1/Rn
• The equivalent resistance is smaller than the smallest resistance: Req < R1, R2
• In a parallel circuit, voltage stays the same across all branches
• Current divides according to the resistance of each branch

Series Circuits

• Equivalent resistance (Req) of multiple resistors (R1, R2, ..., Rn) connected in series is: Req = R1 + R2 + ... + Rn
• The equivalent resistance is greater than the largest resistance: Req > R1, R2
• In a series circuit, the current remains the same throughout all components
• Voltage divides among the components

Measuring Current & Voltage

• A multimeter as voltmeter can measure the voltage difference between two points before and after a consumer
• Start with a large range and reduce it step-by-step for accuracy
• Measurement of current using a multimeter works like voltage measurement
• The ohmmeter is connected parallel to the consumer
• The circuit must be open (no current flow) when measuring resistance

Elecrical Energy & Power

• Power is energy per time: P = E/t = qV/t = IV
• Using definition of resistance: P = V²/R = I²R
• SI unit of power is Watt (W)
• Electrical Energy: E = Pt = VI*t
• The SI unit is Joule (J). But it is very common to use kilowatt-hour if electrical energy is taken
• 1 kWh = 3.6 * 10^6 J

Home Electricity

• Standard socket includes the line conductor (L), neutral line (N) and protective earth (PE)

Direct Current (DC)

• Current always flows in the same direction (+ to -)
• Voltage is constant (e.g., 9V)
• Typical voltage source: Batteries
• Typical consumers: Laptop, Phone, TV

Alternating Current (AC)

• Current direction changes a few times per second (Frequency = 50 Hz)
• Voltage alternates (e.g., mean value of 230 V)
• Typical voltage source: Socket
• Typical consumers: Light bulb, Induction stove

Socket Functionalities

• Current flows through hot conductor (L) and neutral conductor (N)
• In a standard socket, hot terminal has a high electric potential, and neutral terminal has a low electric potential (near ground)
• Current flows from the hot terminal to the neutral terminal when a circuit is completed

Electrical Definitions

• Neutral line (Nullleiter) (N): Potential = 0 V
• Line Conductor / Phase (Phase / Aussenleiter) (L): Mean potential = 230 V, alternates between +- 325 V, Frequency = 50 Hz
• Protective Earth / Ground (PE): Potential = 0 V

Health Risks

• Death, muscle cramp, and burns can result from electric shock
• Electric shock can be fatal at current of 30 mA
• Risks include direct contact with live parts (electric shock and burns), arcing, faulty electrical equipment (fire), and unsuitable electrical apparatus (explosion)

Safety Measures

• Circuit Breaker (Fuse): Controls current, interrupts circuit if it becomes too high (short circuit), prevents fires and damage, is located in the fuse box
• Residual Current Device (RCD): Controls current in line and N, ensuring they are equal, interrupts circuit if leakage current occurs (through person or faulty ground wire) to prevent electric shock

Protective Earth

• Electrical devices with metallic housings should be connected to the ground conductor
• Prevents housing from becoming electrified, reducing shock hazard

Troubleshooting

• If a circuit breaker or RCD trips, unplug devices and reset the switch
• Contact an electrician if the cause is unclear

Phase Tester

• Consists of a high-value resistor (to reduce the current) and a bulb
• A measuring instrument that can measure the phase difference and time difference of synchronous signals in the power system
• If the user closes the circuit via the body, a current can flow if a voltage is bigger than 0V is applied, therefore the lamp will shine brighter