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Inessa [10]
2 years ago
7

Please answer !!!A company wants to install a sensor to monitor the light level in the offices of their buildings. The sensor co

ntains an LDR which has a resistance of 10kohlms in daylight and 100kohlms in the dark . The choice of resistor in the circuit is between one of 25kohlms and 1 megaohlm. The input p.d to the sensing circuit of 12 v . State and explain which resistor is the best choice for the circuit in light and dark which each of the resistors . You could put your calculations in a table .
Physics
2 answers:
vovikov84 [41]2 years ago
3 0

Answer:

Explanation:

The sensor contains an LDR which has a resistance of 10kohlms in daylight and 100kohlms in the dark.

If the resistor in the circuit is 1 megaohlm, the total resistance in daylight and darkness will be 1.01 megaohms and 1.1 megaohlms.

The percentage difference = (1.1-1.01)/1.1*100% = 8.18%

If the resistor in the circuit is 25 kohlm, the total resistance in daylight and darkness will be 35 kohms and 125 kohlms.

The percentage difference = (125-35)/125*100% = 72%

With the input p.d to the sensing circuit fixed at 12 v, the sensing current will change according to the total resistance. A 72% difference is much more detectable. So the 25 kohm resistor is the better choice.

dem82 [27]2 years ago
3 0

Answer:

Explanation:

V=IR

I=12/(R of resistor + R of LDR)

R of LDR = 10kohm in light and = 100kohm in dark

R1 =  25kohm

R2 = 1Mohm

solve 4 current

                       light                                       dark

R1        12/(25+10)=0.343mA          12/(25+100)=0.096mA

R2       12/(1000+10)=0.012mA       12/(1000+100)=0.011mA

so R1 is better as its easier 2 tell its light or dark

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aev [14]

Answer:

evaporation

Explanation:

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B. Is faster in solids than liquids would be the correct answer because the molecules in solids are much closer and can pass along energy faster and more effectively.
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An aluminum-alloy rod has a length of 10.0 cm at 20°C and a length of 10.015 cm at the boiling point of water (1000C). (a) What
nikitadnepr [17]

Answer:

a.  9.99625 cm b. 68 °C

Explanation:

(a) What is the length of the rod at the freezing point of water (0 0C)?

Before we find the length of the rod, we need to find the coefficient of linear expansion, α = (L - L₀)/[L₀(T - T₀)] where L₀ = length of rod at temperature T₀ = 10.0 cm, T₀ = 20 °C, L = length of rod at temperature T = 10.015 cm and T = 100 °C

Substituting the values of the variables into the equation, we have

α = (L - L₀)/[L₀(T - T₀)]

α = (10.015 cm - 10.0 cm)/[10.0 cm(100 °C - 20 °C)]

α = 0.015 cm/[10.0 cm × 80 °C]

α = 0.015 cm/[800.0 cm °C]

α = 0.00001875 /°C

We now find the length L₁ at T₁ = 0 °C from

L₁ = L₀(1 + α(T₁ - T₀))

So, substituting the values of the variables into the equation, we have

L₁ = L₀(1 + α(T₁ - T₀))

L₁ = 10.0 cm[1 +  0.00001875 /°C(0° C - 20 °C)]

L₁ = 10.0 cm[1 +  0.00001875 /°C × -20° C]

L₁ = 10.0 cm[1 - 0.000375]

L₁ = 10.0 cm[0.999625]

L₁ = 9.99625 cm

(b) What is the temperature if the length of the rod is 10.009 cm?

With length L₃ = 10.009 cm at temperature T₃, using

L₃ = L₀(1 + α(T₃ - T₀))

making T₃ subject of the formula, we have

L₃/L₀ = 1 + α(T₃ - T₀)

L₃/L₀ - 1 = α(T₃ - T₀)

T₃ - T₀ = (L₃/L₀ - 1)/α

T₃ = T₀ + (L₃/L₀ - 1)/α

substituting the values of the variables into the equation, we have

T₃ = 20 °C + (10.009 cm/10.0 cm - 1)/0.00001875 /°C

T₃ = 20 °C + (1.0009 - 1)/0.00001875 /°C

T₃ = 20 °C + 0.0009/0.00001875 /°C

T₃ = 20 °C + 48 °C

T₃ = 68 °C

8 0
3 years ago
A baseball rolls off of a .7 m high desk and strikes the floor .25 m always how fast was the ball rolling
labwork [276]

Answer:

the ball's velocity was approximately 0.66 m/s

Explanation:

Recall that we can study the motion of the baseball rolling off the table in vertical component and horizontal component separately.

Since the velocity at which the ball was rolling is entirely in the horizontal direction, it doesn't affect the vertical motion that can therefore be studied as a free fall, where only the constant acceleration of gravity is affecting the vertical movement.

Then, considering that the ball, as it falls covers a vertical distance of 0.7 meters to the ground, we can set the equation of motion for this, and estimate the time the ball was in the air:

0.7 = (1/2) g t^2

solve for t:

t^2 = 1.4 / g

t = 0.3779  sec

which we can round to about 0.38 seconds

No we use this time in the horizontal motion, which is only determined by the ball's initial velocity (vi) as it takes off:

horizontal distance covered = vi * t

0.25 = vi * (0.38)

solve for vi:

vi = 0.25/0.38  m/s

vi = 0.65798  m/s

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4 0
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The speed of a nerve impulse in the human body is about 100 m/s. If you accidentally stub you toe in the dark, estimate the time
vodomira [7]

Answer:

0.02 s

Explanation:

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The average velocity v during a time interval Δt is the displacement Δx divided by Δt.  

v=Δx/Δt

 =x_f-x_i/t_f-t_i                 (1)

We assume that your height is 1.6m  

Solving [1]

Δt=Δx/v

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3 years ago
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