Chapter-4 Electricity — Online MCQ Test
SCIENCE · Grade 8 · CBSE(NCERT)
Practice Chapter-4 Electricity with a free chapter-wise online MCQ test.
This chapter covers: electric current - heating effect - magnetic effect - electromagnet - fuse - electric circuit - resistance.
AI-generated questions from basic to board-exam level, with instant results and explanations.
Chapter-4 Electricity — Important Questions & Answers
What is electric current?
- A. The flow of electrons through a conductor
- B. The amount of charge flowing per unit time
- C. The resistance in a circuit
- D. The voltage across a conductor
Answer: B. The amount of charge flowing per unit time
Electric current is defined as the amount of electric charge flowing through a cross-section of a conductor per unit time.
Electric current is defined as the amount of electric charge flowing through a cross-section of a conductor per unit time.
Which unit is used to measure electric current?
- A. Volt
- B. Ampere
- C. Ohm
- D. Watt
Answer: B. Ampere
Electric current is measured in Amperes (A), named after physicist André-Marie Ampère.
Electric current is measured in Amperes (A), named after physicist André-Marie Ampère.
What is the heating effect of electric current called?
- A. Joule heating
- B. Thermal conduction
- C. Convection
- D. Radiation effect
Answer: A. Joule heating
The heating produced when electric current flows through a conductor is called Joule heating or Joule effect, discovered by James Joule.
The heating produced when electric current flows through a conductor is called Joule heating or Joule effect, discovered by James Joule.
Which device uses the heating effect of electric current?
- A. Electric heater
- B. Electric motor
- C. Ammeter
- D. Electromagnet
Answer: A. Electric heater
Electric heaters use the heating effect of current, where resistance in the heating element produces heat.
Electric heaters use the heating effect of current, where resistance in the heating element produces heat.
Which of the following is NOT a component of an electric circuit?
- A. Power source
- B. Conductor
- C. Magnetic field
- D. Switch
Answer: C. Magnetic field
A basic electric circuit requires a power source, conductors, and a switch, but a magnetic field is not a necessary component of the circuit itself.
A basic electric circuit requires a power source, conductors, and a switch, but a magnetic field is not a necessary component of the circuit itself.
A bulb becomes brighter when connected to a battery. This demonstrates which effect of electric current?
- A. Magnetic effect only
- B. Heating effect only
- C. Both heating and magnetic effects
- D. Neither heating nor magnetic effect
Answer: B. Heating effect only
A bulb becomes bright due to the heating effect of electric current, where the filament heats up and emits light.
A bulb becomes bright due to the heating effect of electric current, where the filament heats up and emits light.
An electric bell works on the principle of:
- A. Heating effect of current
- B. Magnetic effect of current
- C. Chemical effect of current
- D. Light emission
Answer: B. Magnetic effect of current
An electric bell uses the magnetic effect of electric current. The electromagnet attracts the armature to produce a ringing sound.
An electric bell uses the magnetic effect of electric current. The electromagnet attracts the armature to produce a ringing sound.
Compare the resistance of two wires: Wire A has length L and diameter d, Wire B has length 2L and diameter 2d. Which wire has greater resistance?
- A. Wire A has greater resistance
- B. Wire B has greater resistance
- C. Both have equal resistance
- D. Cannot be determined without knowing the material
Answer: C. Both have equal resistance
Resistance R = ρL/A. For Wire A: R₁ = ρL/(πd²/4). For Wire B: R₂ = ρ(2L)/(π(2d)²/4) = ρ(2L)/(4πd²/4) = ρL/(πd²/4). Both have equal resistance.
Resistance R = ρL/A. For Wire A: R₁ = ρL/(πd²/4). For Wire B: R₂ = ρ(2L)/(π(2d)²/4) = ρ(2L)/(4πd²/4) = ρL/(πd²/4). Both have equal resistance.
In a circuit, if voltage is doubled while resistance remains constant, what happens to the current?
- A. Current is halved
- B. Current doubles
- C. Current remains the same
- D. Current becomes zero
Answer: B. Current doubles
According to Ohm's law (V = IR), if voltage doubles and resistance is constant, current must double to maintain the equation.
According to Ohm's law (V = IR), if voltage doubles and resistance is constant, current must double to maintain the equation.
Three identical resistors of 6Ω each are connected in series. What is the total resistance? If the same resistors are connected in parallel, what is the total resistance?
- A. Series: 18Ω; Parallel: 2Ω
- B. Series: 6Ω; Parallel: 18Ω
- C. Series: 18Ω; Parallel: 6Ω
- D. Series: 2Ω; Parallel: 18Ω
Answer: A. Series: 18Ω; Parallel: 2Ω
Series: R_total = 6 + 6 + 6 = 18Ω. Parallel: 1/R_total = 1/6 + 1/6 + 1/6 = 3/6 = 1/2, so R_total = 2Ω.
Series: R_total = 6 + 6 + 6 = 18Ω. Parallel: 1/R_total = 1/6 + 1/6 + 1/6 = 3/6 = 1/2, so R_total = 2Ω.