Parallel Circuits

How are components connected in a parallel circuit?

• All the components are connected in a single loop

• Parallel circuits do not contain components

• The components are not connected at all

• Each component is connected on a different branch

Answer explanation

In a parallel circuit, components are connected on different branches.  There are multiple paths for current to flow. 

What happens when the switch is closed? 

• Only the bottom lamp turns on

• Both lamps turn on at the same time

• Only the top lamp turns on

• The top lamp turns on and then the bottom lamp turns on

Answer explanation

Current flows through both branches of the parallel circuit. Both lamps turn on at the same time. 

Two identical lamps are connected in parallel. How bright are the lamps? 

• The top lamp is the brightest

• The lamps are the same brightness

• Both lamps are off

• The bottom lamp is the brightest

Answer explanation

The lamps have the same potential difference across them. The lamps are identical so they have the same resistance. The same amount of current flows through them. 

The lamps are the same brightness.

What happens to the bottom lamp if the top lamp breaks? 

• The bottom lamp gets dimmer

• The bottom lamp gets brighter

• The bottom lamp turns off

• The bottom lamp stays the same brightness

Answer explanation

The same amount of current still flows through the bottom lamp. The bottom lamp stays the same brightness.

Which statement correctly describes the current in a parallel circuit? 

• The total current into a junction equals the total current out of a junction

• The total current into a junction is less than the total current out of a junction

• The total current into a junction is more than the total current out of a junction

• The current is the same in all parts of the circuit

Answer explanation

The total current into the junction equals the total current out of that junction.  

4A = 2A + 2A 

Which of these circuits are parallel circuits?

• X and Y only

• X and Z only

• Y and Z only

• all of them

Answer explanation

Z has no junctions / branches and therefore is a series circuit

Which switches must be pressed to make bulb X

come on?

• 1 and 2 only

• 1 and 3 only

• 2 and 3 only

• all three of them

Answer explanation

Closing switches 1 and 2 completes a circuit which includes bulb X

Parallel circuits are used for house lights:

• so they can all be switched on and off together.

• so you know when one breaks, because all the

  others go off.

• so they use a bigger current.

• so they can all be switched on and off

  separately.

Which of these statements is not true?

• The currents at Q and R add up to give the

  current at S.

• The current is the same at P and S.

• The current is the same at Q and R.

• The current is the same at P and Q.