Page 5 - 1202 Question Bank Physics Form 5

MUST

KNOW Common Mistakes

Resolution of Forces Current-carrying Conductor
• The diagram below shows a current-carrying conductor placed
Wrong Correct
in a magnetic field.
F = 100 sin 30°
x y I
F = 100 cos 30°
Vertical component 30° 100 N find the angle with the horizontal N S
labelled.©PAN ASIA PUBLICATIONS
or
line first:
100 N

Wrong
Correct
60° • State the direction of the force on the conductor.
F = 100 cos 30°
x Horizontal line Fleming’s right-hand rule The current-carrying conductor
F = 100 sin 30°
y is used to determine the is not an induced current, so need
F = 100 sin 30° or 100 cos 60°
x direction of force. to use Fleming’s left-hand rule to
F = 100 cos 30° or 100 sin 60°
y determine the direction of the force.
Common Mistakes (Chapter 1) 37 @ Pan Asia Publications Sdn. Bhd. Common Mistakes (Chapter 4) 43 @ Pan Asia Publications Sdn. Bhd.
Total Pressure Effect of Magnetic Field on Cathode Rays

What is the ratio of the pressure at X to the pressure at Y? • The diagram below shows a Maltese cross tube.
Cathode Anode Maltese
Wrong Correct cross
Air +
P 20 m H O P Shadow
Water x 2 x
20 m P = 30 m H O P –
30 m y 2 y Filament
= 2 : 3 (10 + 20) m H O
2
X =
(10 + 30) m H O
2
Y • What will happen to the velocity of the cathode ray if the
= 3 : 4
potential difference, V between the cathode and the anode is
Note: Total pressure = Atmospheric pressure + pressure due to water increased?
Wrong Correct
No change 2eV
Cathode rays velocity, v =  , thus
m
the velocity increases as V increases.
Common Mistakes (Chapter 2) 39 @ Pan Asia Publications Sdn. Bhd. Common Mistakes (Chapter 5) 45 @ Pan Asia Publications Sdn. Bhd.
Magnetic Field Working Functions for Photoelectric Effects

Wrong Correct If the threshold wavelength is 420 nm, calculate the metal working
function in units of eV.
• The electric • The electric
field lines – field lines Wrong Correct
incorrectly + are always +
directed away Students solve this question by Students need to simplify the
from positive using equation: photoelectric equation:
• Positively charges. hc 1
2
charged l = mv + W W = hf o
2
particles – • The electric
field lines are
• Negatively always directed –
charged toward negative
particles charges.

 Common Mistakes (Chapter 3) 41 @ Pan Asia Publications Sdn. Bhd. Common Mistakes (Chapter 7) 47 @ Pan Asia Publications Sdn. Bhd.

Must know_1202 Physic F5.indd 7 07/01/2022 11:41 AM