Current electricity

What is the unit of electric current?

• Ampere
• Volt
• Coulomb
• Ohm

Answer explanation

The ampere (A) is the SI unit of electric current, which measures the rate of flow of electric charge.

Which of the following are true about electric current? (Select all that apply)

• It's the rate of flow of charge
• It's measured in amperes
• It's always constant
• Conventional current flows from positive to negative

Answer explanation

Current is the rate of flow of charge, measured in amperes. Conventional current is defined as flowing from positive to negative, although electrons actually flow in the opposite direction.

Fill in the blank: The relationship between charge, current, and time is Q = ___ × ___

Answer explanation

The correct formula is Q = I × t, where Q is charge, I is current, and t is time.

What does e.m.f. stand for in electrical circuits?

• Electromotive force
• Electrical magnetic field
• Electron movement factor
• Energy motion flow

Answer explanation

E.m.f. stands for electromotive force, which is the work done per unit charge by a source in driving charges around a complete circuit.

If three 1.5V batteries are connected in series, what is the total e.m.f.?

• 4.5V
• 1.5V
• 3V
• 0.5V

Answer explanation

When batteries are connected in series, their voltages add up. So, 1.5V + 1.5V + 1.5V = 4.5V

Explain the difference between e.m.f. and potential difference in your own words.

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Draw a simple circuit diagram showing a battery, two resistors in series, and an ammeter measuring the current.

If the p.d. across a resistor is 12V and the current through it is 2A, what is its resistance?

• 6O
• 24O
• 10O
• 14O

Answer explanation

Using R = V / I, we get: 12V / 2A = 6O

• 0.09A
• 90A
• 0.9A
• 10A

Answer explanation

Using I = V / R, we get: 9V / 100O = 0.09A

Explain why birds sitting on high-voltage power lines don't get electrocuted.

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