Electricty and safety

• Natuurkunde
• Middelbare school
• vwo
• Leerjaar 3

Take in front of you:

Laptop + calculator

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Electrical power is:

1. Energy per unit of time
2. a synonyme for energy
3. Energy times time
4. the strength of a machine

An engine offering 6 kJ in one minute has a power of:

1. 10 W
2. 10 J/s
3. 100 W
4. 100 J/s

The correct and complete supply chain of electrical energy looks like:

1. power station - grid - house
2. house - power station - transformer substation
3. power station - grid - transformer substation - house
4. power station - transformer substation - grid - house

In one 'group' ...

1. the voltage is the same everywhere
2. the voltage can vary
3. the current is the same everywhere
4. none of the above

What are the dangers of electricity?

Dangers of electricity

• The current through the wires gets too high                                                                 --> Danger of fire!                                                                    Caused by overloading or short-circuiting                                                                                                           
• Current from a wire can run through your body                                          --> Can be deadly above 1A! (see table 1)                                                        Caused by loose or broken wires 

Overloading

• Too many devices running on a group at the same time. 
• The group draws to much power (too many joules/second). 
• The current goes above the safety limit (16 A). 
  
• The wire heats up to much — Fire.

What is the maximum power a group can handle?

Short-circuiting

• The current goes straight from the negative pole to the positive pole with barley any resistance in between. 
  
• This causes too big a current to flow to the wire.
  
• The wire hets up to much — Fire.
  

Fuses

Earth leakage circuit breakers

Earthing

The symbol for current, and the symbol for its unit are:

1. I and W
2. I and J
3. I and A
4. P and W

A circuit breaker . . .

1. compares the incoming current to the outgoing current
2. measures the incoming current
3. measures the outgoing current
4. is a manually operated switch

Which one is
the earthing
(grounding) wire?

1. The black one
2. The brown one
3. The yellow/green one
4. The blue one

Make:

• Chapter 1 section 4.