Numerical Problems Based on Errors in Measurements for Class 11 Physics

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Numerical Problems on Error Analysis

Class 11 Physics · Units and Measurements
SQ

Error Calculation Practice Set

Apply formulas for mean, absolute error, relative error, and percentage error
Ch 2 · Units and Measurements
1
The diameter of a wire as measured by a screw gauge was found to be $0.026 \text{ cm}, 0.028 \text{ cm}, 0.029 \text{ cm}, 0.027 \text{ cm}, 0.024 \text{ cm}$ and $0.027 \text{ cm}$. Calculate (i) mean value of the diameter (ii) mean absolute error (iii) relative error (iv) percentage error. Also express the result in terms of absolute error and percentage error.
Answer (i) $0.027 \text{ cm}$ (ii) $0.001 \text{ cm}$ (iii) $\pm 0.037$ (iv) $\pm 3.7\%$; Result: $(0.027 \pm 0.001) \text{ cm}$, $(0.027 \pm 3.7\%) \text{ cm}$ 📝
Detailed Solution

(i) Mean value of diameter ($d_m$):

$$d_m = \frac{0.026 + 0.028 + 0.029 + 0.027 + 0.024 + 0.027}{6}$$
$$d_m = \frac{0.161}{6} = 0.02683 \approx 0.027 \text{ cm}$$

(ii) Mean absolute error ($\Delta d_m$):

Calculate the absolute errors ($|\Delta d_i| = |d_i – d_m|$):
$|\Delta d_1| = |0.026 – 0.027| = 0.001$
$|\Delta d_2| = |0.028 – 0.027| = 0.001$
$|\Delta d_3| = |0.029 – 0.027| = 0.002$
$|\Delta d_4| = |0.027 – 0.027| = 0.000$
$|\Delta d_5| = |0.024 – 0.027| = 0.003$
$|\Delta d_6| = |0.027 – 0.027| = 0.000$

$$\Delta d_m = \frac{0.001 + 0.001 + 0.002 + 0.000 + 0.003 + 0.000}{6}$$
$$\Delta d_m = \frac{0.007}{6} = 0.00116 \approx 0.001 \text{ cm}$$

(iii) Relative error:

$$\text{Relative error} = \pm \frac{\Delta d_m}{d_m} = \pm \frac{0.001}{0.027} = \pm 0.037$$

(iv) Percentage error:

$$\text{Percentage error} = \pm 0.037 \times 100\% = \pm 3.7\%$$

Final Results:
In terms of absolute error: $(d_m \pm \Delta d_m) = (0.027 \pm 0.001) \text{ cm}$
In terms of percentage error: $(0.027 \text{ cm} \pm 3.7\%)$

2
The refractive index of water as measured by the relation $\mu = \frac{\text{Real depth}}{\text{Apparent depth}}$ was found to have the values $1.29, 1.33, 1.34, 1.35, 1.32, 1.36, 1.30, 1.33$. Calculate (i) mean value of $\mu$ (ii) mean value of absolute error (iii) relative error (iv) percentage error.
Answer (i) 1.33 (ii) 0.02 (iii) $\pm 0.015$ (iv) $\pm 1.5\%$ 📝
Detailed Solution

(i) Mean value of $\mu$ ($\mu_m$):

$$\mu_m = \frac{1.29 + 1.33 + 1.34 + 1.35 + 1.32 + 1.36 + 1.30 + 1.33}{8}$$
$$\mu_m = \frac{10.62}{8} = 1.3275 \approx 1.33$$

(ii) Mean absolute error ($\Delta\mu_m$):

Calculate the absolute errors ($|\Delta\mu_i| = |\mu_i – \mu_m|$):
$|1.29 – 1.33| = 0.04$
$|1.33 – 1.33| = 0.00$
$|1.34 – 1.33| = 0.01$
$|1.35 – 1.33| = 0.02$
$|1.32 – 1.33| = 0.01$
$|1.36 – 1.33| = 0.03$
$|1.30 – 1.33| = 0.03$
$|1.33 – 1.33| = 0.00$

$$\Delta\mu_m = \frac{0.04 + 0.00 + 0.01 + 0.02 + 0.01 + 0.03 + 0.03 + 0.00}{8}$$
$$\Delta\mu_m = \frac{0.14}{8} = 0.0175 \approx 0.02$$

(iii) Relative error:

$$\text{Relative error} = \pm \frac{\Delta\mu_m}{\mu_m} = \pm \frac{0.02}{1.33} = \pm 0.01503 \approx \pm 0.015$$

(iv) Percentage error:

$$\text{Percentage error} = \pm 0.015 \times 100\% = \pm 1.5\%$$
3
In an experiment to measure focal length of a concave mirror, the value of focal length in successive observations turns out to be $17.3 \text{ cm}, 17.8 \text{ cm}, 18.3 \text{ cm}, 18.2 \text{ cm}, 17.9 \text{ cm}$ and $18.0 \text{ cm}$. Calculate the mean absolute error and percentage error. Express the result in a proper way.
Answer MAE: $0.25 \text{ cm}$, % Error: $\pm 1.4\%$, Result: $(17.9 \pm 0.25) \text{ cm}$ 📝
Detailed Solution

Mean value of focal length ($f_m$):

$$f_m = \frac{17.3 + 17.8 + 18.3 + 18.2 + 17.9 + 18.0}{6}$$
$$f_m = \frac{107.5}{6} = 17.916 \approx 17.9 \text{ cm}$$

Mean absolute error ($\Delta f_m$):

Calculate the absolute errors ($|\Delta f_i| = |f_i – f_m|$):
$|17.3 – 17.9| = 0.6$
$|17.8 – 17.9| = 0.1$
$|18.3 – 17.9| = 0.4$
$|18.2 – 17.9| = 0.3$
$|17.9 – 17.9| = 0.0$
$|18.0 – 17.9| = 0.1$

$$\Delta f_m = \frac{0.6 + 0.1 + 0.4 + 0.3 + 0.0 + 0.1}{6}$$
$$\Delta f_m = \frac{1.5}{6} = 0.25 \text{ cm}$$

Percentage error:

$$\text{Relative error} = \frac{\Delta f_m}{f_m} = \frac{0.25}{17.9} = 0.01396$$
$$\text{Percentage error} = \pm 0.01396 \times 100\% \approx \pm 1.4\%$$

Result expression:

$$(f_m \pm \Delta f_m) = (17.9 \pm 0.25) \text{ cm}$$

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