30 degrees
60 degrees
+Q1
Physics 201
TEST 1
084
NAME:_________________________
Given a tablespoon ( 15 cm
3
) of water, find :
What is the mass of one tablespoon of water is ( assume the density of water is 1000kg/m
3
)
V
water
15cm
3
=
The density of water is
ρ
water
1000
kg
m
3
=
the mass of water in
is
m
water
ρ
water
V
water
⋅
=
m
water
15gm
=
What is the charge due to the electrons on 1 molecule of water?
The number of electrons in one molecule of water( H
2
O) is the sum of electrons in 2 atoms of
hydrogen ,
N
e_H
1
=
,and the nuimber of electrons in one atom of oxygen,
N
_e_O
8
=
so
N
e_water
2
N
e_H
⋅
N
_e_O
+
=
N
e_water
10
=
so the charge due to the elecrrons
in 1 molecule of water is
Q
H20
10
1.602

10
19

C
⋅
(
29
⋅
=
Q
H20
1.602

10
18

×
C
=
What is the total charge due to all the electrons in 15 cm
3
of water?
so
We determine the number of moles of water in a volume of
V
water
15cm
3
=
M
mol_H
1amu
=
The molecular mass of hydrogen is
The molecular mass of 0xygen is
M
mol_O
16amu
=
The molecular mass of water
is
M
mol_water
2 M
mol_H
⋅
M
mol_O
+
=
M
mol_water
18amu
=
The number of moles of water is
n
water
m
water
M
mol_water
=
n
water
0.833 mol
=
The number of water molecules is
N
water
N
a
n
water
⋅
=
N
water
5.017
10
23
×
molecules
=
The total electrons is
N
e
N
water
N
e_water
⋅
=
N
e
5.017
10
24
×
electrons
=
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x
y

Q2
30
0
30
0

Q3
*
Given the dipole below of charge Q and separation “a”
Determine the E field
(magnitude and direction) at a point “P” along the perpendicular axis of the dipole
E
plus
E
neg
Q
4
π
⋅
ε
0
⋅
a
2
2
R
2
+
⋅
the only component that survives is the
+ycomponent
E
y_plus
E
plus
(
29
sin
θ
(
29
⋅
where
sin
θ
(
29
a
2
a
2
2
R
2
+
1
2
E
totaL
→
2
Q
4
π
⋅
ε
0
⋅
a
2
2
R
2
+
⋅
⋅
a
2
a
2
2
R
2
+
1
2
⋅
j
→
⋅
E
totaL
→
Q a
⋅
4
π
⋅
ε
0
⋅
a
2
2
R
2
+
3
2
⋅
j
→
⋅
What direction would the force on an electron placed at “P” be in?
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 Spring '11
 Gilbert
 Electron, Charge, Electrostatics, Mass, Electric charge

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