Day 3.3ForceFields

1)Sometimes you can exert forces without contact.
a) How can you pick up bits of paper without touching?
b) How can you pick up paper clips without touching?

c) How can you pick up a ball without touching?

2)Watch MinutePhysics: Real World Telekinesis. How does telekinesis work?
3)A magnetic field around a magnet can be made visible by iron filings.
a)Predict and then sketch the magnetic field around a bar magnet.

b)Predict and then observethe field between two north poles.

c)Predict and then observe the field between a north and a south pole.

4)The Earth produces a gravitational field, g = F/m.

a)Sketch thegravitational field lines in the classroom.How can you make these field lines visible?

b) What are the units of the gravitational field?

c) Calculate the field, g = Fg/m,near the surface of the Earth. (rE = 6.38 x 106 m, ME = 5.98 x 1024 kg)
d) What do gravitational field lines around the Earth look like?
e) What would the field lines between the Earth-Moon system look like? How can you model this with magnets and iron fillings?
f) How does the field strength vary inside the Earth? Hint: What is the value at the centre?
5)Electrical charges produce a field, E = F/Q.
a) What will the electric field around a charged sphere look like?What gravitational field is this like?

.

b) What will the electric field near two opposite charges look like? How can you show this with a balloon a person with long hair? How can you model this with two magnets and filings?
c)What will the electric field near two similar charges look like? How can you show this with two balloons? How can you model with two magnets and filings?
d) What will the field inbetween parallel charged plates look like? What gravitational field is this similar to?
e) How is it the field of a hollow spherical conductor similar to and different from that of the Earth?Look at p. 381 Figure 7 and p. 346 Figures 20-23.

f) What is the formula for the electrical field, E= Fe/q, around a point or spherical charge? Hint: What is the formula for the gravitational field arounda point or spherical mass?

6)Watch Electric field inside a conductor. Tesla Cage of Death is a Faraday cage and how does it protect you? Where are they used?

7)Stretchy fabric can be used to model fields. How would you model the field of;

a)a planet or charged sphere?

b)the Moon-Earth system.

c)a magnetic or electric dipole

8)Go to Phet level 1 with just 2 charges.

Textbook 7.3, 8.1p. 347 # 8-10