Electricity

Case Study 1: Ohm's Law

Case Description:
Ohm's Law states that the current flowing through a conductor between two points is directly proportional to the voltage across the two points, provided the temperature remains constant. This relationship can be expressed with the formula $V = IR$, where $V$ is the voltage, $I$ is the current, and $R$ is the resistance.

MCQs:

1. According to Ohm's Law, if the resistance in a circuit is constant, what happens to the current if the voltage increases?

   • A) The current decreases
   • B) The current remains the same
   • C) The current increases
   • D) The current becomes zero

2. If a circuit has a voltage of 10 V and a resistance of 5 Ω, what is the current flowing through the circuit?

   • A) 0.5 A
   • B) 2 A
   • C) 5 A
   • D) 10 A

3. What is the unit of resistance?

   • A) Volt
   • B) Ampere
   • C) Ohm
   • D) Watt

4. If the voltage across a resistor is doubled, what happens to the current through it, assuming resistance remains constant?

   • A) It halves
   • B) It doubles
   • C) It remains the same
   • D) It becomes zero

Case Study 2: Series and Parallel Circuits

Case Description:
In a series circuit, all components are connected end-to-end, so the same current flows through each component. In a parallel circuit, all components are connected across the same voltage source, so the voltage across each component is the same, and the total current is the sum of the currents through each path.

MCQs:

1. In a series circuit, if one component fails, what happens to the rest of the circuit?

   • A) Only that component stops working
   • B) The entire circuit remains functional
   • C) The entire circuit stops working
   • D) The circuit becomes a parallel circuit

2. In a parallel circuit, if one branch is disconnected, what happens to the other branches?

   • A) They stop functioning
   • B) They continue to function
   • C) The total current decreases to zero
   • D) They become series circuits

3. Which of the following statements is true about total resistance in a series circuit?

   • A) It is less than the smallest resistance
   • B) It is the sum of all individual resistances
   • C) It remains constant
   • D) It is equal to zero

4. What is the formula for calculating total resistance ($R_t$) in a parallel circuit?

   • A) $R_t = R_1 + R_2 + R_3$
   • B) $\frac{1}{R_t} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3}$
   • C) $R_t = R_1 \times R_2 \times R_3$
   • D) $R_t = R_1 - R_2 - R_3$

Case Study 3: Electrical Power and Energy

Case Description:
Electrical power is the rate at which electrical energy is consumed or converted into other forms of energy. It is given by the formula $P = VI$, where $P$ is power in watts, $V$ is voltage in volts, and $I$ is current in amperes. Electrical energy consumed can also be calculated using the formula $E = Pt$, where $E$ is energy in joules and $t$ is time in seconds.

MCQs:

1. If a device operates at a voltage of 120 V and draws a current of 2 A, what is the power consumed by the device?

   • A) 60 W
   • B) 120 W
   • C) 240 W
   • D) 480 W

2. How is electrical energy typically measured?

   • A) Joules
   • B) Watts
   • C) Ohms
   • D) Volts

3. If an electrical appliance consumes 1000 W of power for 2 hours, how much energy does it consume in kilowatt-hours (kWh)?

   • A) 1 kWh
   • B) 2 kWh
   • C) 3 kWh
   • D) 4 kWh

4. What happens to the power consumed if the voltage is doubled while keeping the resistance constant?

   • A) Power halves
   • B) Power remains the same
   • C) Power doubles
   • D) Power quadruples

Case Study 4: Electrostatics and Current

Case Description:
Electrostatics is the study of electric charges at rest. When two materials are rubbed together, electrons may transfer from one material to another, resulting in static electricity. This can lead to phenomena like lightning, where a large buildup of static charge discharges rapidly.

MCQs:

1. What is the fundamental unit of electric charge?

   • A) Coulomb
   • B) Ampere
   • C) Volt
   • D) Ohm

2. When a rubber rod is rubbed with fur, what type of charge does the rubber rod acquire?

   • A) Positive charge
   • B) Negative charge
   • C) Neutral charge
   • D) Indeterminate charge

3. Which of the following is an example of electrostatic discharge?

   • A) Flow of current in a circuit
   • B) The shock you feel when touching a doorknob after walking on a carpet
   • C) Lighting a bulb
   • D) Powering an electric fan

4. The electric field strength around a charged object is:

   • A) Directly proportional to the amount of charge and inversely proportional to the square of the distance
   • B) Inversely proportional to the amount of charge and directly proportional to the square of the distance
   • C) Constant at all distances
   • D) Independent of the amount of charge

Case Study 5: Applications of Electricity

Case Description:
Electricity has numerous applications in our daily lives, from household appliances to industrial machines. Understanding circuits and electrical components is essential for the safe and effective use of electrical devices. Safety measures such as fuses and circuit breakers are critical in preventing electrical hazards.

MCQs:

1. What is the primary purpose of a fuse in an electrical circuit?

   • A) To increase voltage
   • B) To decrease current
   • C) To protect against excessive current
   • D) To convert AC to DC

2. In an electrical circuit, what device is used to interrupt the flow of current in case of an overload?

   • A) Resistor
   • B) Circuit breaker
   • C) Capacitor
   • D) Inductor

3. Which of the following devices converts electrical energy into mechanical energy?

   • A) Electric bulb
   • B) Electric motor
   • C) Transformer
   • D) Resistor

4. If an electrical appliance has a power rating of 500 W and is used for 3 hours, how much energy does it consume in kilowatt-hours (kWh)?

   • A) 0.5 kWh
   • B) 1.5 kWh
   • C) 2.0 kWh
   • D) 3.0 kWh