# Switches

## Basic Electricity

• #### Question 1

What is the purpose of the switch shown in this schematic diagram?

• #### Question 2

How is an electrical switch constructed? What goes on inside the switch that actually “makes” or “breaks” a path for electric current?

• #### Question 3

What difference will it make if the switch is located in either of these two alternate locations in the circuit?

• #### Question 4

Does this switch (in the closed state) have a low resistance or a high resistance between its terminals?

• #### Question 5

How might you use a meter (or a conductivity/continuity tester) to determine whether this electrical switch is in the open or closed state?

• #### Question 6

Identify the following types of switches, according to the number of “poles” and “throws” each switch has:

• #### Question 7

Identify the following types of switches, according to their style of actuation (how each switch is physically operated):

• #### Question 8

What type of switch is represented by this schematic symbol?

• #### Question 9

What type of switch is represented by this schematic symbol?

• #### Question 10

What positions do the switches have to be in for the light bulb to receive power?

• #### Question 11

Electric motors of the permanent magnet design are very simple to reverse: just switch the polarity of the DC power to the motor, and it will spin the other direction:

Complete this schematic diagram, showing how a DPDT switch may be placed in this circuit to reverse the motor’s direction of rotation without the need to disconnect and re-connect wires:

• #### Question 12

What will the light bulb do when the switch is open, and when the switch is closed?

• #### Question 13

Examine this schematic diagram:

Now, without moving the following components, show how they may be connected together with wires to form the same circuit depicted in the schematic diagram above:

• #### Question 14

What does the normal status of an electrical switch refer to? Specifically, what is the difference between a normally-open switch and a normally-closed switch?

• #### Question 15

Identify the “normal” status of each switch, whether it is normally-open (N.O.) or normally-closed (N.C.):

Based on the symbols shown, describe what physical condition results in the switch contacts being open, and what condition results in the switch contacts being closed, for each switch.

• #### Question 16

Identify the “normal” status of each switch, whether it is normally-open (N.O.) or normally-closed (N.C.):

Based on the symbols shown, describe what physical condition results in the switch contacts being open, and what condition results in the switch contacts being closed, for each switch.

• #### Question 17

Identify the “normal” status of each switch, whether it is normally-open (N.O.) or normally-closed (N.C.):

Based on the symbols shown, describe what physical condition results in the switch contacts being open, and what condition results in the switch contacts being closed, for each switch.

• #### Question 18

Find one or two real switches and bring them with you to class for discussion. Identify as much information as you can about your switches prior to discussion:

• Number of poles
• Number of throws
• Voltage rating of contacts
• Current rating of contacts
• Contact status for various actuator positions
• Type (toggle, pushbutton)