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Basic Electrical Practice

Electrician Trade Theory, Module-4

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By Roni
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Basic Electrical Practice

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Q1: How many electrons are there in the third cell of the copper atom?

  • 8
  • 13
  • 18
  • 29

Q2: Which is the semiconductor material?

  • Eureka
  • Ebonite
  • Manganin
  • Germanium

Q3: What is the indication of neon polarity indicator used for checking A.C. supply?

  • Both electrodes will glow
  • Only one electrode will glow
  • Both electrodes will be flickering
  • One electrode will glow and another will be flickering

Q4: Calculate the electrical energy in unit consumed by 500W lamp for 5 hours.

  • 0.5 unit
  • 1.0 unit
  • 1.5 unit
  • 2.5 unit
Show Calculation \[ \text{Energy} = \frac{500 \times 5}{1000} = 2.5 \text{ units} \]

Q5: What is the value of hot resistance of a bulb rated as 100W/250V?

  • 31.25 ohm
  • 62.50 ohm
  • 312.50 ohm
  • 625.00 ohm
Show Calculation \[ R = \frac{V^2}{P} = \frac{250^2}{100} = \frac{62500}{100} = 625\,\Omega \]

Q6: Which law states that in closed electric circuit, the applied voltage is equal to the sum of the voltage drops?

  • Ohm’s law
  • Laws of resistance
  • Kirchhoff’s first law
  • Kirchhoff’s second law

Q7: Calculate the total power of the circuit of two lamps rated as 200W/240V are connected in series across 240V supply?

  • 100 W
  • 50 W
  • 200 W
  • 400 W
Show Calculation \[ R = \frac{V^2}{P} = \frac{240^2}{200} = 288\,\Omega \quad \text{(per lamp)} \]\[ \text{Total resistance} = 576\,\Omega \]\[ I = \frac{240}{576} = 0.416\,\text{A} \]\[ P = I^2 \times R = (0.416)^2 \times 576 \approx 100\,W \]

Q8: What is the formula for the equivalent resistance (RT) of the three resistors R1, R2 & R3 connected in parallel circuit?

  • \(R_T = R_1 + R_2 + R_3\)
  • \(R_T = \frac{R_1 R_2 R_3}{R_1 + R_2 + R_3}\)
  • \(R_T = \frac{R_1 + R_2 + R_3}{3}\)
  • \(\frac{1}{R_T} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3}\)

Q9: What is the reading of ohmmeter across opened ‘R2’ resistor?

circuit diagram
  • Indicate zero reading
  • Indicate infinite resistance
  • Total resistance value of the circuit
  • Value of sum of the resistance of R1 and R3 only

Q10: What is the change of resistance value of the conductor as its diameter is doubled?

  • Increases to two times
  • Decreases to four times
  • Decrease to half of the value
  • No change in value of resistance
Show Calculation \[ R \propto \frac{1}{A} \quad \text{and} \quad A \propto d^2 ~ \text{If } d \rightarrow 2d, \] \[ \text{ then } A \rightarrow 4A \Rightarrow R \rightarrow \frac{R}{4} \]

Q11: What is the name of the resistor?

wire wound resistor
  • Metal film resistor
  • Wire wound resistor
  • Carbon – film resistor
  • Carbon composition resistor

Q12: Calculate the resistance value of the resistor by colour coding method.

Resistor
  • \(23 \times 10^3\,\Omega \pm 5\%\)
  • \(26 \times 10^3\,\Omega \pm 10\%\)
  • \(32 \times 10^4\,\Omega \pm 10\%\)
  • \(37 \times 10^4\,\Omega \pm 5\%\)
Show Resistance Calculator

Q13: Why the ohmmeter is graduated with non-linear scale?

ohmmeter
  • Voltage is directly proportional to resistance
  • Current is inversely proportional to resistance
  • Resistance is inversely proportional to the square of current
  • Voltage is directly proportional to the square of the current

Q14: Calculate the value of unknown resistance ‘RDC’ in the Wheatstone bridge network, if PAB = 500 Ω, QBC = 300 Ω, SAD = 15 Ω at balanced condition.

Wheatstone bridge
  • 12 Ω
  • 9 Ω
  • 6 Ω
  • 3 Ω
Show Calculation \[ R_{DC} = \frac{Q_{BC} \times S_{AD}}{P_{AB}} = \frac{300 \times 15}{500} = 9\,\Omega \]

Q15: Which material is having negative temperature co-efficient property?

  • Mica
  • Eureka
  • Copper
  • Manganin

Q16: What electrical quantities are related in Ohm’s law?

  • Current, resistance and power
  • Current, voltage and resistivity
  • Current, voltage and resistance
  • Voltage, resistance and current density

Q17: Calculate the value of resistance R2 in the parallel circuit.

Parallel circuit
  • 2 Ω
  • 4 Ω
  • 6 Ω
  • 8 Ω
Show Calculation

\[I_1 = \frac{24}{8} = 3\,\text{A}, \quad I_3 = \frac{24}{3} = 8\,\text{A}\]

\(I_2 = 15 - 3 - 8 = 4\,\text{A}\)

\(R_2 = \frac{24}{4} = \boxed{6\,\Omega}\)

Q18: What is the effect of the parallel circuit with one branch opened?

  • Current will remain same
  • Whole circuit will not function
  • No current will flow in that branch
  • Voltage drop increase in the opened branch

Q19: What is the unit of resistivity?

  • ohm / cm
  • ohm / cm²
  • ohm · metre
  • ohm / metre

Q20: Which type of resistor is used for Arc quenching protection in circuit breakers?

  • Varistors
  • Sensistors
  • Thermistors
  • Light dependent resistor (LDR)

Q21: Calculate the value of resistance by colour coding method.

Resistor with color
  • \(22 \times 10^3\,\Omega \pm 10\%\)
  • \(23 \times 10^4\,\Omega \pm 10\%\)
  • \(25 \times 10^3\,\Omega \pm 5\%\)
  • \(36 \times 10^4\,\Omega \pm 5\%\)
Show Resistance Calculator

Q22: Calculate the unknown resistance “RDC” in the Wheatstone bridge circuit, if \(P_{AB}=400\,\Omega\), \(Q_{BC}=200\,\Omega\) and \(S_{AD}=12\,\Omega\) at balanced condition.

Wheatstone bridge Calculation
  • 4 Ω
  • 6 Ω
  • 8 Ω
  • 12 Ω
Show Calculation Using: \[ \frac{P_{AB}}{Q_{BC}} = \frac{S_{AD}}{R_{DC}} \]\[ \Rightarrow R_{DC} = \frac{Q_{BC} \times S_{AD}}{P_{AB}} = \frac{200 \times 12}{400} = 6\,\Omega\]

Q23: What is the reading of the voltmeter ‘V’?

circuit diagram with voltmeter
  • 0 V
  • 6 V
  • 9 V
  • 18 V

Q24: Which is the application of series circuit?

  • Voltmeter connection
  • Lighting circuits in home
  • Shunt resistor in ammeter
  • Multiplier resistor of a voltmeter

Q25: What is the effect on opened resistor in series circuit?

  • No effect in opened resistor
  • Full circuit current will flow in opened resistor
  • Total supply voltage will appear across the opened resistor
  • No voltage will appear across the opened resistor

Q26: Calculate the resistance value in R3 resistor.

3 Resistor in parallel
  • 4 Ω
  • 6 Ω
  • 8 Ω
  • 12 Ω
Show Calculation \[ R_{total} = \frac{V}{I} = \frac{24}{12} = 2\,\Omega \] For resistors in parallel: \[ \frac{1}{R_{total}} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} \] \[\Rightarrow \frac{1}{2} = \frac{1}{4} + \frac{1}{6} + \frac{1}{R_3} \] \[ \Rightarrow \frac{1}{2} - \frac{1}{4} - \frac{1}{6} = \frac{1}{R_3} \] \[ \Rightarrow \frac{6 - 3 - 2}{12} = \frac{1}{R_3} \] \[ \Rightarrow \frac{1}{R_3} = \frac{1}{12} \] \[ \Rightarrow R_3 = 12\,\Omega \]

Q27: What is the effect of the circuit, if ‘ab’ points are shorted?

Resistors in parallel
  • Circuit resistance will be zero
  • Same current will flow in all branches
  • Supply voltage will exist in each branch
  • Total circuit current is equal to each branch circuit current

Q28: What is the name of the resistor if its resistance value increases with increase in temperature?

  • Varistors
  • Sensistors
  • Thermistors
  • Light Dependent Resistor (LDR)

Q29: What is the formula for Quantity of electricity (Q)?

  • Current × Time
  • Voltage × Current
  • Current × Resistance
  • Voltage × Resistance
Show Explanation \(Q = I \times t\)

Q30: What is the unit of conductance?

  • Mho
  • Ohm
  • Ohm-m
  • Ohm/m

Q31: Which one defines the change in resistance in Ohm (Ω) per degree centigrade (°C)?

  • Temperature effect
  • Laws of temperature
  • Temperature constant
  • Temperature co-efficient

Q32: Which type of meter is used to test the polarity of battery?

  • Moving iron ammeter
  • Moving coil voltmeter
  • Moving iron voltmeter
  • Dynamo meter type wattmeter

Q33: What is the voltage drop in resistor ‘R2’ in the series circuit?

series circuit
  • 5 Volt
  • 10 Volt
  • 15 Volt
  • 20 Volt
Show Calculation \[I = \frac{V_{\text{total}}}{R_{\text{total}}} = \frac{50\,\text{V}}{1000\,\Omega} = 0.05\,\text{A}\] \[V_{R_2} = I \times R_2 = 0.05\,\text{A} \times 200\,\Omega = 10\,\text{V}\]

Q34: Which is the application of series circuit?

  • Fuse in circuit
  • Voltmeter connection
  • Electrical lamp in homes
  • Shunt resistor in ammeter

Q35: Which method is used for measuring 1 Ohm to 100K Ohm range resistance?

  • Substitution method
  • Kelvin bridge method
  • Wheat stone bridge method
  • Voltmeter and ammeter method

Q36: What is the S.I unit of specific resistance?

  • \(\Omega/\text{cm}\)
  • \(\Omega/\text{metre}^2\)
  • \(\Omega\cdot\text{metre}\)
  • \(Micro ohm/cm²\)

Q37: What is the value of resistance of the resistor?

color code of resistance
  • 330 ± 5% Ohm
  • 3300 ± 10% Ohm
  • 33000 ± 5% Ohm
  • 330000 ± 10% Ohm
Show Resistance Calculator

Q38: What is the purpose of the shunt resistor ‘R2’ used in series type Ohm meter circuit?

ohmmeter in series circuit
  • To limit the current in the circuit
  • To increase the value of meter resistance
  • To adjust the zero position of the pointer
  • To prevent the excess current in the circuit

Q39: Which electrical quantity affects the heat generated in a conductor?

  • Voltage
  • Square of the current
  • Square of the resistance
  • Current passed through it
Show Explanation \[Joule's Law: H \propto I^2 R t \]

Q40: What is the change in value of resistance of the conductor, if its cross section area is doubled?

  • No change
  • Decreases 2 times
  • Increases 2 times
  • Decreases 4 times
Show Calculation \[Since~ R \propto \frac{1}{A}\]\[ doubling~ A \Rightarrow R ~becomes~half \]

Q41: Calculate the voltage drop across the resistor ‘R4’ in the circuit.

voltage drop across the resistor
  • 48 V
  • 72 V
  • 80 V
  • 100 V
Show Calculation \[\frac{1}{R_{23}} = \frac{1}{R_2} + \frac{1}{R_3} = \frac{1}{40} + \frac{1}{60}\] \[\frac{1}{R_{23}} = \frac{3 + 2}{120} = \frac{5}{120} = \frac{1}{24} \Rightarrow R_{23} = 24\,\Omega\] \[R_{\text{total}} = R_1 + R_{23} + R_4 = 36 + 24 + 50 = 110\,\Omega\] \[I = \frac{V_{\text{total}}}{R_{\text{total}}} = \frac{220}{110} = 2 \] \[\text{A}V_{R_4} = I \times R_4 = 2 \times 50 = \boxed{100\,\text{V}}\]

Q42: What is the resistance of Light Dependent Resistor (LDR), if the intensity of light is increased?

  • Increases
  • Decreases
  • Remains same
  • Becomes infinity

Q43: Which formula is used to calculate the power of a DC circuit?

  • Voltage × time
  • Current × voltage
  • Current × resistance
  • Voltage × resistance
Show Explanation \[ P = V \times I \]

Q44: Calculate the hot resistance of 200W / 250V rated lamp.

  • 31.25 Ω
  • 62.5 Ω
  • 312.5 Ω
  • 625 Ω
Show Calculation \[ R = \frac{V^2}{P} = \frac{250^2}{200} = 312.5\,\Omega \]

Q45: What is the value of resistance in an open circuit?

  • Zero
  • Low
  • High
  • Infinity

Q46: Which resistor the lowest current flows in a parallel circuit having the values of 50 Ω, 220 Ω, 450 Ω and 560 Ω connected with supply?

  • 50 Ω
  • 220 Ω
  • 450 Ω
  • 560 Ω
Show Explanation \[In parallel: I \propto \frac{1}{R} \] \[ → Highest~ resistance = lowest~current \]

Q47: What is the specific resistance value of copper conductor?

  • 1.72 Ohm/cm³
  • 1.72 Micro ohm
  • 1.72 Micro ohm.m
  • 1.72 Micro ohm.cm

Q48: Which is inversely proportional to the resistance of a conductor?

  • Length
  • Resistivity
  • Temperature
  • Area of cross section
Show Explanation \[ R \propto \frac{l}{A} \Rightarrow R \propto \frac{1}{A} \text{ when length is constant} \]
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1st year, Trade Theory
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