Mechanism
Mechanism
Electricity
Electricity
100
True or False? A lever is a rigid bar that can pivot on a point of support called a fulcrum.
True.
100
How many motion conversion mechanisms have we learnt?(25 extra points for naming each one!)
Four.(screw and nut, rack and pinion, crank and slider, cam)
100
Name one conductor.
Gold, silver, aluminium, copper, steel, iron...
100
Name one control device.
One-way switch/Push switch/Two-way switch
200
How many types of levers have we learnt?
There are three types of levers, depending on the position of the applied force, fulcrum and resistance.
200
True or False? The characteristics of crank and slider is that it is irriversible.
False. We can make the slider the driver and have it turn the crank.
200
What is the structure of an atom?
An atom consists of a central nucleus containing positively charged protons and uncharged (neutral) neutrons, surrounded by orbiting, negatively charged electrons.
200
What are the main variables in Ohm's law?
Current, voltage and resistance.
300
What is the formula of transmission ratio(i)?
The transmission ratio(i) is the ratio between the size of the wheels and the speed of rotation:
i = omega_1 / omega_2 = d_2 / d_1
300
Name one example of screw and nut mechanism in daily life.
Vehicle jacks, taps, lipsticks...
300
Name four main components in an electric circuit and draw a circuit with all of them.
power sources, conductors, load devices, control devices.
300
What is voltage and what is the unit?
Voltage (or potential difference) is the difference in the charge between two points, which makes the electron move. Its unit of measurement is volt(V).
400
In a gear, the driver wheel has 30 teeth and the driven wheel has 60 teeth. The driver wheel rotates at 300 rpm. Indicate whether is a speed reducing mechanism or a speed multiplying mechanism, and why?
The transmission ratio(i) = z2 / z1 = 60/30 = 2. Since the transmission ratio is greater than 1, it is a speed reducing mechanism.
400
Fill in the blanks: Cams are usually ________ in shape. They are attached to a ______ shaft and as they rotate, they drive an element called the _______.
(score will only be given if all answers are correct)
elliptical, driver, follower.
400
What is Ohm's law and what is the equation of it?
Ohm's law states the current in a circuit is directly proportional to the electric potential difference impressed across its ends and inversely proportional to the total resistance offered by the external circuit.
I = V/R
400
Explain what is a parallel circuit and one advantage of using it.
Parallel circuit is a circuit that the load devices are connected on different branches of the wire.
500
Explain what is a worm gear.
It is a rotary transmission mechanism consists of a worm(driver), that only has one spiral tooth, and a toothed/worm wheel(driven).
500
Explain all the chacracteristics and name one application of rack and pinion.
It is a very smooth and precise mechanism.
It is reversible: the driver element can be either the pinion or the rack.
It is used in corkscrews, garage doors, drill presses, trains that travel up steep inclines...
500
Calculate the I.
We know the total potential of this circuit,
V =12.0V
V1=V2=V3=V=12.0V
We can use Ohm's Law
V=IR
or
I=V/R
to find the current across each resistor.
I1=V1/R1=12.0V/2.0Ω=6.0A
I2=V2/R2=12.0V/3.0Ω=4.0A
I3=V3/R3=12.0V/6.0Ω=2.0A
So, adding up the three currents, we get:
I=I1+I2+I3
=6.0+4.0+2.0=12.0A
So, the total current is I=12.0A.
500
Is this circuit open, closed or shorted?
Closed. (I think)