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so in today's lesson we're going to
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do
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physical question paper for grade 10 and
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then in this question we're going to
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look at firstly the multiple choice
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question
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whereby we supposed to find
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um the following they're saying The
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pulse A is moving to the right with
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amplitude Y m overlaps with pulse B
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moving to the left with amplitude 1 / Y
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m so remember pulse A is moving to the
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right and P B is moving to the left and
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then the amplitude is given by Y m and
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then also the amplitude of B is given by
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1 / 2 Y
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m so
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now we have to find um at the point
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where which of the following combination
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will be correct when the PS meet at the
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media so now the upper direction is
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positive and then the downward direction
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is negative so it's going to be y 1 y -
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1
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y it's going to be
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1us2 y
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and then we can see
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that
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um it's constructive because the
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positive direction the upper direction
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is the constructive is the the positive
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one is the constructive
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interference and the negative part is
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the destructive interference and then
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whenever we look at our final answer our
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final answer is positive so means that
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it's a constructive interference of 0
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y and option C is the correct
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one so now which of the following is
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correct for the sound waves so let's
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look at
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option so
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um which of the following is correct for
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sound
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waves option A travel faster in gases
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than
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solids and let's look at option D
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travels through the particle
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so it travels faster in a gas than in a
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solid let's look at solids whenever you
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look at solids
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love waves can never pass through a
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solid but in a gas but let's look at
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vacuum veum is like air whenever I'm
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talking right now my sound is moving
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through air this means that option A is
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definitely correct and then let's look
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at option
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B I mean option C travel faster at low
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temperatures now and
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then waves
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remember those ones and then sound waves
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are represented by this is an example of
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sound so this means that option is the
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correct so let's look
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at formulas now formulas of sound waves
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just go to your formula sheet it's
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always given the back of the
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formula so we're going to use table two
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wave sound so this are the
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formulas so now let's look at what is
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given the time it takes from a to which
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is m the period the time
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mc and then we also we're looking for
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the
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frequenc let's look at formula we're
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given the
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velocity the frequency we don't have
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velocity you can even see in the
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question we don't
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velocity option and then energy you not
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given the energy in the formula And then
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obviously the constant given but the
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energy is the
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thing that option is on and also that's
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an energy question
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so you're left with given t the period
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and then we're looking for we can use
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that t =
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1 and then we can substitute our t which
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is
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mcute m = 1 f and then we can solve for
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f make f the formula we say
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one cross multip
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* fn = 2 1 * 1 which is 1
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/ both cosides therefore f = 1 m x
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so this is our answer therefore option d
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is the correct one option is the correct
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answer for this question remember look
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at what's given look at what's given
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we're given the
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period then we're looking for f let's
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clarify option
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D now which of the inject becoming
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positive
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charactions let's look at
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magnesium and magnesium 2
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plus magnesium
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2+ so what are N ions and what are K
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ions
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so what we know about ke ions keions
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um are particles that are negatively
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charged and non is a particle that is
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negatively charged so is a is a charged
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particle that is that is made by gaining
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of
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electrons so it becomes negatively
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charged so let's use magnesium magnesium
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G2 minus it gained electron so it's an N
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it's a negative charge so it gained
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electrons so cines will become will
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basically be the opposite so will
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basically just
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say is a charged particle that is made
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by the loss of electrons so this is a ke
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so let's look at our option positively
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charged loss loses electron so option B
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is the in this
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case option B is the correct let's look
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at question 1.5 question
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1.5 it talks about in the second diagram
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the resistance resistor E
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is which of the following is correct the
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charge resistor A talking about the
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charge and the charge resistor A and the
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charge through resistor
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B so now what is the
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charge so now let's talk about the 10
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charge what is charge in this case so
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now let's go to
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electricity a
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charge you have to understand what is a
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charge a charge is
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measured so let's look at =
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= I
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* I is the charge
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i is always the charge so we have we
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have a definition of a
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charge
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so a charge
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um is the
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rate I mean current is the rate of
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charge meaning current I is current
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which is measured in
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amp so now
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This rate of charge is basically it's
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like it's taken is derived from Q
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= I * so I * T then make I the subject
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of the
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formula and then I
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= Q / delta T this means that I is the
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rate of charge q is
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charge q is the
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charge and then delta T so let let me
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try making this symbol so from from the
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formula we're just going to make I as
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our charge the subject and divide by
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delta
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T and then I will be given by Q over
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delta T that's the
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rate of charge
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this is the rate of charge this is
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basically the current the definition of
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a current when I say define what is
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currently just saying current is the
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rate of
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charge current is the rate of charge
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my
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screen so we here current is the rate of
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charge and then which is measured in
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appears
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a and then let's look at the two
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formulas they both consist of
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I they both have I let's look at the
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other formula which is V = I *
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R so they both have R so let's make I
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the subject
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I divide by
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R this are the two formulas of current
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which is the length of charge so we'll
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choose between the it depends on what
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the for what do we want so now we given
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the resistance so which formula will you
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use given R so the formula we'll be
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using it's I = V /
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R so in this case we're going to ignore
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V because it's not given so just in the
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case of you put
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one of for the charge of A we use
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one 2
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I and then in the place of current of B
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so this is basically 1 / two right and
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then this is going to be 1 which is one
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so the charge of B is one and the charge
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of A is 1 /2 option
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[Music]
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A so the
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charge we were saying that the
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charge through A option A the charge
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through A is double the charge this
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means that this is definitely wrong the
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charge through resistor A is half the
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charge of resistor B which is two we
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already calculated
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that so let's look at question two
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question two is the tricky one this is
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the tricky
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question we're given the frequency and
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the
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speed of this question
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so we're going to define what is a
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transverse
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wave so a transverse wave
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is a transverse
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wave is a is a wave in which the
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distribution the distribution is at
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right angle to the direction of the
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propagation of
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a
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so you will see if we put a if we put a
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particle
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here and then the direction the
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direction of the medium is to the right
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you can see that the the charge is at
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right angle to the propagation of the
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medium this means that that's the
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definition of the transverse wave so x
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is the wavelength y is the amplitude
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now the main
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question given the frequency and the
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velocity you're supposed to find the
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length so going to use the
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first the first equation which says that
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V
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= 10
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= *
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lambda
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for going to divide by 20 on both sides
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both
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sides 5
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m so yeah the next question says
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that determine the time between point A
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to point
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B determine the time between A and B
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here we have many ways to
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calcate so we have two formulas we are
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supposed to find the period
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t and then we're supposed to
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plot so there are many so what is the
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distance between a to b a to b how many
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waves are here so we have the first
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[Music]
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wave the second wave and the third wave
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so in this case we have three waves so
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point A to B will move three
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times so this means
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that the is going to be three times the
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wave so the wavelength from A to B is
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going to be 3 *
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0 which is 1 5
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m and then another one we already know
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the speed the speed of the wave it's
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given as 10
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m/s the speed is given as 10
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m/s so now we already have the
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velocity we already have the lambda
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supposed to find the frequency find the
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frequency velocity
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= * frequency 10
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= 0 5 * frequency then you can solve for
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f is equals
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to this is it's going to be 1
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66 I mean
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66 yeah 6a 66
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her and then now we have the the
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frequency we can use the period for 1 /
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f therefore
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= 15 seconds now 0 seconds it's going to
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be 0 5 seconds this is the frequency so
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there's also another method so let's try
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let's try and see what's happening what
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is happening here the first
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thing we have to use what's given on 2 I
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mean what we calculated on 2.3 so when
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we got wrong on 2.31 the whole thing is
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wrong so we have wave number one wave
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number two and wave number three
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so the first thing you have to know is
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the
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distance you have to know that from A to
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B is three times the wavelength and
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another thing is the
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speed this is method number two we're
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going to use distance equals to speed
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over
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time distance equals to speed over time
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we have distance as 1 5 and velocity as
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I mean as and speed as 10
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m/s we can
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say now this is speed equals to
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distance and then we already have the
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speed we already have the speed the
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distance The distance is 1.5 and the
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speed is
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10 so now we can substitute and find
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time this is method number
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two this is method number two guys don't
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get
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confused you have many ways to
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calcate two ways so velocity is
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10 v can put a 10 and then there is
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distance you can put 1 5
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m you can just cross
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multiply time is equals
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to 0a
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5
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seconds thanks
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guys um this is the end of the
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lesson and this is method number two
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just a reminder guys method two we have
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method number one hands
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