P.3.5.1.1 Basics of electricity

Which is equivalent to the ohm?

• J C^–2 s^–1

• J C^–2 s

• J s

• J s^–1

A gas containing doubly-charged ions flows to give an electric current of 0.64 A

How many ions pass a point in 1.0 minute?

• 2.0 × 10¹⁸

• 4.0 × 10¹⁸

• 1.2 × 10²⁰

• 2.4 × 10²⁰

Three cells each have an emf ε = 1.5 V and an internal resistance r = 0.6 Ω.

Which combination of these cells will deliver a total emf of 1.5 V and a maximum current of 7.5 A?

• A

• B

• C

• D

The current in the cell is 10 A as shown

What is the current in the 2.0 Ω resistor?

• 0.35 A

• 2.86 A

• 3.50 A

• 7.14 A

The units of physical quantities can be expressed in terms of the fundamental (base) units of the SI system. In which line in the table are the fundamental units correctly matched to the physical quantity?

• A

• B

• C

• D

A metal wire has a length l and a cross-sectional area A. When a potential difference V is applied to the wire, there is a current I in the wire.

What is the resistivity of the wire?

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• 
• 
• 

When a constant potential difference (pd) is applied across the ends of a uniform wire there is a current I in the wire.

The wire is replaced by one made from the same material, but of double the length and double the diameter. The same pd is applied across the ends.

What is the new current?

• 4I

• 2I

• I/2

• I/4

A pd V is applied across a resistor. Another identical resistor is then connected in series with it and the same pd V is applied across the combination.

Which statement is incorrect?

• The total resistance is doubled

• The pd across one resistor is V/2

• The current in the resistors is halved.

• The power dissipated in one resistor is halved.

The cell in the following circuit has an emf of 2.0 V and an internal resistance of 1.0 Ω.

The digital voltmeter reads 1.6 V. What is the resistance of R?

• 0.4 Ω

• 1.0 Ω

• 2.0 Ω

• 4.0 Ω

A horizontal copper wire of mass 4.0 × 10⁻³ kg and length 80 mm is placed perpendicular to a horizontal magnetic field of flux density 0.16 T. The magnetic force acting on the wire supports the weight of the wire.

How many electrons are passing a point in the wire in each second?

• 1.9 × 10¹⁸

• 1.9 × 10¹⁹

• 1.9 × 10²⁰

• 1.9 × 10²¹